RPC-UHF [RADIOMETRIX]
Radio Packet Controller; 无线分组控制器
| 型号： | RPC-UHF |
| 厂家： | 
RADIOMETRIX LTD |
| 描述： | Radio Packet Controller |
| 文件： | 总28页 (文件大小：711K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Radiometrix
Issue 4, 25 July 2001
RPC-UHF
Radio Packet Controller
Modules: RPC-418-40: IC+BiM, UK version
RPC-433-40: IC+BiM, Euro version
IC’s:
RPC-000-DIL:
RPC-000-SO:
18 pin DIL IC
18 pin SO IC
The
RPC-418-40
and
RPC-433-40
are
intelligent transceiver modules which enable
a radio network/link to be simply implemented
between a number of digital devices. The
module combines a UHF radio transceiver
and a 40kbit/s packet controller.
The RPC-module
• SAW controlled FM transmitter and superhet receiver
• Reliable 30 meter in-building range, 120m open ground
• Built-in self-test / diagnostics / status LED’s
• Complies with ETSi 300-220 regulations
• Single 5V supply @ < 20mA
• 40kbit/s half duplex
• Free format packets of 1 - 27 bytes
• Packet framing and error checking are user transparent
• Collision avoidance (listen before transmit)
• Direct interface to 5V CMOS logic
• Power save mode
INTRODUCTION
The RPC is a self-contained plug-on radio port which requires only a simple antenna, 5V supply and a
byte-wide I/O port on a host microcontroller (or bi-directional PC port).
The module provides all the RF circuits and processor intensive low level packet formatting and packet
recovery functions required to inter-connect an number of microcontrollers in a radio network.
A data packet of 1 to 27 bytes downloaded by a Host microcontroller into the RPC's packet buffer is
transmitted by the RPC’s transceiver and will "appear" in the receive buffer of all the RPC's within
radio range.
A data packet received by the RPC’s transceiver is decoded, stored in a packet buffer and the Host
microcontroller signalled that a valid packet is waiting to be uploaded.
figure 1: RPC + Host µ-controller
Radiometrix Ltd, RPC
page 1
Radiometrix Ltd, RPC
page 2
1. FUNCTIONAL DESCRIPTION
On receipt of a packet downloaded by the Host, the RPC will append to the packet: Preamble, start
byte and a error check code. The packet is then coded for security and mark:space balance and
transmitted through the BiM Transceiver as a 40kbit/s synchronous stream. One of four methods of
collision avoidance (listen before TX) may be user selected.
When not in transmit mode, the RPC continuously searches the radio noise for valid preamble. On
detection of preamble, the RPC synchronises to the in-coming data stream, decodes the data and
validates the check sum. The Host is then signalled that a valid packet is waiting to be unloaded. The
format of the packet is entirely of the users determination except the 1st byte (the Control Byte) which
must specify the packet type (control or data) and the packet size. A valid received packet is presented
back to the host in exactly the same form as it was given.
To preserve versatility, the RPC does not generate routing information (i.e.
source/ destination addresses) nor does it handshake packets. These
network specific functions should be performed by the host.
Additional features of the RPC include extensive diagnostic/debug functions for evaluation and
debugging of the radio and host driver software, a built in self test function and a sleep mode / wake-up
mechanism which may be programmed to reduce the average current to less than 100µA. The
operating parameters are fully programmable by the host and held in EEPROM, the host may also use
the EEPROM as a general purpose non-volatile store for addresses , routing information etc.
1.1 OPERATING STATES
The RPC has four normal operating states:
•
•
•
•
IDLE / SLEEP
HOST TRANSFER
TRANSMIT
RECEIVE
IDLE/SLEEP
The IDLE state is the quiescent/rest state of the RPC. In IDLE the RPC enables the receiver and
continuously searches the radio noise for message preamble. If the power saving modes have
been enabled the RPC will pulse the receiver on, check for preamble and go back to SLEEP if
nothing is found. The 'ON' time is 5ms, OFF time is programmable in the RPC’s EEPROM and
can vary between 22ms and 2.9s. The TX Request line from the Host is constantly monitored
and will be acted upon if found active (low). A TX Request will immediately wake the RPC up
from SLEEP mode.
HOST TRANSFERS
If the host sets the TX Request line low a data transfer from the Host to the RPC will be
initiated. Similarly the RPC will pull RX Request low when it requires to transfer data to the
Host (this may polled or used to generate a Host interrupt ).
The transfer protocol is fully asynchronous, i.e. the host may service another interrupt and
then continue with the RPC transfer. It is desirable that all transfers are completed quickly
since the radio transceiver is disabled until the Host <> RPC transfer is completed. Typically a
fast host can transfer a 27 byte packet to / from the RPC in under 1ms.
Radiometrix Ltd, RPC
page 3
TRANSMIT
On receipt of a data packet from the host, the RPC will append to the packet - preamble, frame
sync byte and an error check sum. The packet is then coded for mark:space balance and
transmitted. A full 27 byte packet is transmitted in 13.8ms of TX air time (40kb/s + 5ms
preamble).
Collision avoidance (Listen Before Transmit-LBT) functions can be enabled to prevent loss of
packets.
Data packets may be sent with either normal or extended preamble. Extended preamble is
used if the remote RPC is in power save mode. Extended preamble length can be changed in
the EEPROM memory.
RECEIVE
On detection of preamble from the radio receiver, the RPC will phase lock, decode and error
check the incoming synchronous data stream and if successful. The data is then placed in a
buffer and the RX Request line is pulled low to signal to the host that a valid packet awaits to
be uploaded to the Host.
An in-coming data packet is presented back to the host in the same form as it was given.
Radiometrix Ltd, RPC
page 4
2 THE HOST INTERFACE
2.1 SIGNALS
It is recommended that the RPC be assigned to a byte wide bi-directional I/O port on the host
processor. The port must be such that the 4 data lines can be direction controlled without affecting the
4 handshake line.
pin
pin
pin
I/O
description
name number
function
TXR
TXA
6
7
TX Request
TX Accept
I/P
Data transfer request from HOST to RPC
Data accept handshake back to HOST
O/P
RXR
RXA
8
9
RX Request
RX Accept
O/P
I/P
Data transfer request from RPC to HOST
Data accept handshake back to RPC
D0
D1
D2
D3
2
3
4
5
Data 0 (4)
Data 1 (5)
Data 2 (6)
Data 3 (7)
Bi-dir
Bi-dir
Bi-dir
Bi-dir
4 bit bi-directional data bus. Tri-state
between packet transfers, Driven on
receipt for Accept signal until packet
transfer is complete.
notes: 1. The 4 Handshake lines are active low
2. The 4 Data lines true data
3. Logic levels are 5V CMOS, see electrical specifications
4. Input pins have a weak pull-up internally
RESET
The Reset signal, may either be driven by the host (recommended) or pulled up to Vcc via a
suitable resistor (10kΩ). A reset aborts any transfers in progress and restarts the Packet
Controller.
HOST DRIVEN RESET
Minimum low time: 1.0 µs, after reset is released (returned high). The host should allow a
delay 1ms after reset for the RPC to initialise itself
During this delay the host must hold TXR high (unless DIAGNOSTIC MODES are required) and
RXR signal should be ignored.
figure 5: Host to RPC connection
Radiometrix Ltd, RPC
page 5
2.2 HOST TO RPC DATA TRANSFER
Data is transferred between the RPC and the HOST 4 bits (nibbles) at a time using a fully
asynchronous protocol. The nibbles are always sent in pairs to form a byte, the Least Significant
Nibble (bits 0 to 3) is transferred first, followed by the Most Significant Nibble (bits 4 to 7). Two pairs
of handshake lines, REQUEST & ACCEPT, control the flow of data in each direction:-
TX Request & TX Accept:
RX Request & RX Accept:
control the flow from the HOST to the RPC (download)
control the flow from the RPC to the HOST (upload)
A packet transferred between host and RPC consists of between 1 and 28 bytes, the first byte of the
packet is always the control byte.
There are two classes of HOST ↔ RPC transfers:
1. Data Packets:
To the transmitter or from the receiver
2. Memory Access: To or from the RPC's memory
figure 6: RPC ↔ Host data transfer
Radiometrix Ltd, RPC
page 6
2.1.1 WRITE A BYTE TO RPC
The sequence for a byte transfer from the Host to the RPC (i.e. TX download) is asynchronous and
proceeds as follows:
1. HOST asserts TX Request line low to initiate transfer
2. Wait for RPC to pull TX Accept low (i.e. request is accepted)
3. Set data lines to output and place LS nibble on the data lines
4. Negate TX Request (set to 1) to tell RPC that data is present.
5. Wait for RPC to negate TX Accept (i.e. data has been accepted)
Repeat steps 1-5 with MS nibble.
figure 7: TX download timing diagram
Notes:
• The data bus must not be set to output until step 3. i.e. after the RPC has accepted the request. The
bus may be left as an output until the entire packet has been transferred to the RPC, it should then
be set back to input (default state).
• The RPC's normal response time to the initial TX Request may be up to 1ms, thereafter, for the
duration of the packet, the response will be fast.
• The RPC will ignore a TX Request from the Host while it is receiving a packet from the radio. If the
incoming packet fails it's error check the RPC will respond to the TX Request as normal, i.e. the TX
Accept from the RPC will be delayed until the incoming packet has finished. If a valid packet is
received this must be uploaded to the Host before the RPC can respond to the Host’s TX Request.
Thus an RX Request will be signalled to the Host and not the expected TX Accept and the Host
must upload the incoming packet before the TX packet can be downloaded. The TX Request should
be left asserted (low) during the upload. The RPC will respond as normal after the upload is
completed.
• For the above reason it is often easier to use RX Request to trigger a HOST interrupt and upload
the RPC to the HOST under interrupt control.
• See Appendix B and C. for example RPC driver subroutines.
Radiometrix Ltd, RPC
page 7
2.1.2 READ A BYTE FROM THE RPC
The sequence for a byte transfer from the RPC to the HOST (i.e. RX upload) is asynchronous and
proceeds as follows :-
1.
2.
3.
RPC will assert RX Request line low to initiate transfer
Host pulls RX Accept low (i.e. request is accepted by the host)
RPC will turn on it's bus drivers, place LS nibble onto data lines
and negate RX Request (set to 1)
4.
Host reads the data and negates RX Accept (i.e. data has been accepted)
Repeat steps 1-4 with MS nibble.
figure 8: RX upload timing diagram
Notes:
• The RPC will turn off it's data bus drivers after the entire packet has been uploaded to the HOST.
• See Appendix B and C. for example RPC driver subroutines.
2.2 HOST <> RPC PACKET FORMAT
2.2.1 THE CONTROL BYTE
The first byte of a RPC <> HOST packet transfer is always the CONTROL BYTE. This byte is used to
control the transfer and contains information about the type of packet, number of bytes to be
transferred, memory address, read/write bit etc. Bit 7 of the control byte is the Packet Type flag, PT, it
determines the class of transfer and the interpretation of the other bits in the control byte.
Radiometrix Ltd, RPC
page 8
2.2.2 SENDING AND RECEIVING DATA PACKETS
Data packets are sent to / received from remote RPC’s. They begin with a control byte with bit 7
cleared and may be of variable length and contain up to 27 bytes of user determined data.
figure 9: Control byte for data packet
The remainder of the bytes in the data packet are of the users determination.
The packet would usually be made up of a number of fields consisting of some
but not necessarily all of the following :-
Source address / ID
Destination address / ID
System ID
Packet count
Encryption / Scrambler control
Additional error check codes ( The RPC performs it's own error checks)
Routing information ( for repeaters)
Link control codes (connect/disconnect/ACK/NAK etc.)
Data field
2.2.3 RPC MEMORY ACCESS
The RPC’s EEPROM memory can be accessed by setting bit 7 in the control byte. Bit 6 (R/W flag)
defines a memory read or write. The bits left define the address.
figure 10: RPC memory access
Radiometrix Ltd, RPC
page 9
RPC Memory READS:
Host issues just the control byte, with bit 6 (W/R) cleared, bit 7 (PT) set and the memory address. The
RPC will respond with 2 bytes, the first is a control byte which is an echo of the control byte just issued
by the host, this is useful if the host is using an interrupt handler. The 2nd byte is the memory
contents.
RPC Memory WRITES:
Host issues 2 bytes, the first is the control byte with bit 6 (W/R) set, bit 7 (PT) set and the memory
address. The 2nd byte is the data to be written. The RPC does not give a response to memory writes.
figure 11: Control byte for memory access
Notes Memory writes to locations 01 to 3F, write to the non-volatile EEPROM in the RPC. The
EEPROM has a limit of 100,000 write cycles therefor it's use must be
restricted to
infrequently changed data. The RPC only writes to the EEPROM when instructed to by the
HOST. Each byte takes 10ms to write. To prevent accidental/spurious writes to EEPROM the
host must set the WE bit in SWITCHES prior to EACH byte to be written. We recommend that
the host performs a read/verify after each byte write to EEPROM.
The above does not apply to any memory reads nor to writes to SWITCHES (address 00h).
Radiometrix Ltd, RPC
page 10
3.0 RPC’S SWITCHES
SWITCHES is memory location 00h in RAM, it contains 8 flags which are used to determine the RPC's
operation. On RPC reset, power-up or watchdog Time-Out it is loaded from location 08h (in EEPROM).
The default value is 00 hex - this is all functions deselected.
figure 12: Switches
3.1 PS0 & PS1 - POWER SAVING
The RPC has 4 levels of power saving selected by PS0 & PS1 in SWITCHES. Power saving is achieved
by shutting down the Transceiver and the RPC for a period of time (OFF-TIME) when the RPC is in the
Idle state (i.e. nothing happening). During the OFF period current is reduced to the device leakage of
<50 µA typ. The RPC will still respond immediately to a Host TX Request but cannot receive radio
signals. After the programmed OFF-TIME the RPC will wake itself up, turn the receiver on and listen
for valid preamble. ON time = PWR->RX (EEPROM address 05h) + 1ms = 4ms (using RPC Default
values) If preamble is found the RPC will stay ON and decode the packet, if not
the RPC will shut down for another OFF time period.
Also see - WAKE-UP (address 02h of EEPROM) and paragraph 2.2.2 .
Radiometrix Ltd, RPC
page 11
PS1
PS0
0
0
1
1
0
1
0
1
CONTINUOUS 20mA (no power saving)
POWER SAVE
SLEEP
programmable sleeptime *
< 100µA (fixed off time of 2.9s)
OFF
< 50µA Transceiver is off ( reset or TXR to wake-up)
* Sleeptime programmable in EEPROM address 03h.
value
00
off -time
22ms
Average current
2.95 mA
45ms
1.60 mA
01
90ms
0.85 mA
02
181ms
362ms
725ms
1.45s
0.46 mA
03
0.26 mA
04
0.16 mA
05
0.10 mA
06
2.9s
0.08 mA
07
The supply current's quoted above are typical for a BiM + RPC using the
EEPROM default
values.
3.2 HTO & RTO - INTERFACE TIME-OUT
Both the Host and the Radio interfaces can 'hang' the RPC while it
waits for an external event. Under error conditions the RPC will reset
itself if the appropriate HTO or RTO switch is set.
RTO RADIO TIME OUT.
0
1
no time out
Time-Out and reset if > 2.9s of plain preamble detected. (note. valid extended
preamble used for wake-ups will not cause a Time-Out to be detected)
HTO HOST TIME OUT
0
1
no time out
Time-Out and reset if Host fails to reply to any request or handshake
within 2.9s
3.3 WE - EEPROM WRITE ENABLE
This bit protects the EEPROM from accidental writes, it must be set to 1 prior to each byte write to the
EEPROM (addresses 01h to 3Fh). This bit will be cleared by the RPC after each byte write.
3.4 ST - SELF TEST FLAG
Writing a 1 to this switch will initiate a radio self test. Both the transmitter and receiver are enabled,
data is feed to the TX and checked for correct recover from the RX. If the test is good, the ST bit will
set, if the test fails the ST bit will not set. The self test takes 20ms to complete.
Radiometrix Ltd, RPC
page 12
3.5 LBT & DBT - COLLISION AVOIDANCE
Listen Before Transmit, LBT, and Delay Before Transmit, DBT determine what collision avoidance the
RPC will take before each transmission.
LBT DBT Function
0
0
0
1
Immediate TX, no channel check
Fixed delay TX, no channel check (time slots)
This is useful for rapid polling of up to 255 units by a master station.
SLOTS is set to the units ID number, the packet size, preamble length
and change over delay must be the same for all units being polled.
see - EEPROM parameters
1
1
0
1
Immediate TX, if channel is clear
The receiver is turned on and the channel checked for preamble or data.
The RPC will only go to transmit when the channel is clear.
Random delay TX, if channel is clear
This mode is useful in random access networks where there is a high
statistical probability that more than 2 RPCs could be attempting to
transmit at the same time. The receiver is turned on and the channel is
checked for preamble or data. If the channel is clear the RPC will go to
transmit, if the channel is busy the RPC will delay by a random time
(setable by TX-BACK-OFF in EEPROM) then try again for a clear
channel.
Radiometrix Ltd, RPC
page 13
4.0 USER CONFIGURABLE PARAMETERS IN EEPROM
The EEPROM has address range 01h - 3Fh (63 Bytes)
The first 15 BYTES (8 are defined) contain parameters used to control
the RPC.
figure 13: RPC’s EEPROM memory
Radiometrix Ltd, RPC
page 14
PREAMBLE
Number of "01" preamble cycles on TX packets
One '01' cycle takes 50µs @ 40kbit/s
address
01
default
64
formula
valid range
Preamble time = PREAMBLE * 0.05 ms
01 to FF
WAKE-UP
Number of units of 'WAKE-UP PREAMBLE + PLEASE HOLD LINE'
To be sent as extended preamble to wake-up a remote RPC in power
save mode. WAKE-UP should be set to approx. 1.5 times the remote
units OFF Time
address
02
default
FF
formula
valid range
Wake-up message = WAKE-UP * 13.1 ms
01 to FF
SLEEP-TIME
Power Save 'Off' Time (RC controlled)
The OFF time is controlled by an RC oscillator in the RPC which has a
wide tolerance of +/- 30%
03
address
default
05
SLEEP-TIME
formula
valid range
Off-time = 22 * 2
00 to 07
ms
TX ↔ RX
address
TX ↔ RX change over delay in units of 100µs
04
default
1E
formula
Delay = TX ↔ RX * 0.1 ms
valid range
01 to FF
PWR → RX
address:
RX stabilisation delay in units of 100µs
05
default:
1E
formula:
Delay = PWR → RX * 0.1 ms
valid range:
01 to FF
TX-BACK-OFF
Maximum TX Back-off delay in units of 1ms
Used when LBT=1 & DBT=1
06
address
default
03
TX-BACK-OFF
formula
valid range
maximum delay = (2
00 to 07
- 1) ms
00 = 0 - 1 ms
01 = 0 - 3 ms
02 = 0 - 7 ms
03 = 0 - 15 ms
04= 0 - 31 ms
05 = 0 - 63 ms
06 = 0 - 127 ms
07 = 0 - 255 ms
Radiometrix Ltd, RPC
page 15
TX-SLOT
0 - 255 slot number for delayed (polled) TX
Delayed TX in packet units, used when LBT=0 & DBT=1
address
default
formula
07
01
delay = TX-Slot * (Preamble*0.05 + Tpacket + 3*TX ↔ RX + 0.5) ms
where Tpacket = Number of bytes in packet * 0.30 ms
valid range
00 to FF
RESET STATE
RESET STATE OF SWITCHES
The contents of this address are copied into SWITCHES on RPC reset,
power-up or watchdog Time-Out
address
default
08
00
Address 09 to 0F are reserved for future and should not be used by the HOST
EEPROM Addresses 10 TO 3F (48 BYTES) are free for HOST use as general storage.
5.0 DIAGNOSTIC / DEBUG TEST MODES
These special test modes are useful for system testing and debugging
To select these modes the RPC should be released from reset with the TXR line held low, normal RPC
operation will resume when the TXR is set high, i.e. TXR should be held while in these test modes.
figure 14: diagnostic mode selection timing diagram
note: For normal operation of the RPC the TXR line must be held high for either 1ms
after a
reset pulse or 100ms after a power up.
There are 9 test modes which are selected by a binary code applied to the RPC's data bus. A 4 bit DIL
switch or rotary HEX switch connected between the data bus and 0V will select the modes (the RPC
has weak internal pull-up's). Alternatively the HOST may select the test modes by holding TXR low,
resetting the RPC and driving the required test mode code onto the data bus.
note: The RPC continuously monitors the mode selected i.e.. a reset is not required on mode changes.
Radiometrix Ltd, RPC
page 16
In some modes the RXR output from the RPC is driven low to indicate 'pass' or 'OK'. An LED + 1kΩ
from RXR to 5V is recommended.
Mode
Name
RX-ON
RX-PULSE
Function
0
PREAMBLE DETECTOR ON (RXR RED LED = preamble detected)
10ms ON : 10ms OFF, PREAMBLE DETECTOR ON RXR LED
1
2
3
4
5
6
7
8
TX-ON-PRE Preamble Modulation - send continuous preamble
TX-ON-SQ
TX-ON-255
TX-PULSE
ECHO
100Hz SQUARE WAVE MOD - TX testing on spec. Analyser
random 40kbit/s data for EYE DIAGRAM tests, sync's on RXR
10ms ON : 10ms OFF, PREAMBLE BURSTS, RX lock in tests
TRANSPONDER MODE, re-transmit any valid packets received
Send ASCII TEST PACKET "RADIOMETRIX" and listen for echo
Loop test, TX > RX (OK on RXR)
RADAR
SELF-TEST
Modes 6 & 7 are particularly useful for software debugging and range testing.
figure 15: stand-alone diagnostic mode
D3
0
D2
0
D1
0
D0
0
Mode
0
1
2
3
4
5
6
7
8
0
0
0
1
0
0
1
0
0
0
1
1
0
1
0
0
0
1
0
1
0
1
1
0
0
1
1
1
1
0
0
0
Radiometrix Ltd, RPC
page 17
APPENDIX - A
A Detailed look at the RPC's transceiver interface
The RPC interfaces to the transceiver using 4 lines :-
TX
output
Active low enable for the transmitter.
Serial data to be sent.
TXD output
RX output
Active low enable for the receiver.
Received serial data.
RXD input
note 1 All lines are 5V CMOS levels
note 2 There is no requirement for a carrier/signal detect signal from the transceiver nor for the RXD
output to be muted when no signal is present.
The enable lines - TX & RX
These normally high, active low lines are used to control the transceiver. The RPC is a half-duplex
controller thus in normal operation the transceiver is either transmitting or receiving or off. The RPC
only enables the TX and the RX at the same time during self test (local loop back).
Transmit Data - TXD
TXD is the serial data to the transmitter, it is held low when the transmitter is not enabled. When the
TX is enabled a synchronous 40kbit/s (25.0µs/bit) serial code is present to modulate the transmitter.
Receive Data - RXD
RXD is a hi-impedance input which is fed with a 'squared-up' (5V logic level) signal from the receivers'
data slicer. The RPC contains a very selective, noise immune signal detector and therefor does not
require that the RXD signal be muted in the absence of signal, i.e.. squared-up channel noise may be
fed to the RPC when no signal is present.
The RPC's Packet Encoder
The packet is made-up of 4 parts:
Preamble
This is a simple 20kHz square wave, the number of cycles being programmed by address 01h of the
EEPROM. The preamble has two functions, the initial portion it is used to allow the data slicer in a
remote receiver to establish the correct slicing point (for the BiM-XXX-F this takes a maximum of
3ms), after the receiver has settled, the remaining portion is used by the receiving RPC to positively
identify and phase lock onto the incoming the signal (this requires 15 cycles of preamble). The
preamble may extended to wake-up a remote RPC in power saving mode.
Frame sync
A 7 bit Barker sequence is used to identify the start of the data. Alternatively if the transmitter is
sending extended preamble (to wake a power saving remote RPC) a complimented 7 bit Barker
sequence is sent every 256 preamble cycles as a 'Please Hold The Line' code. An 8th balancing bit is
added after the Barker sequence.
Radiometrix Ltd, RPC
page 18
Data
Each byte in the RPC's buffer is expanded into a 12 bit symbol prior to sending. The symbol coding has
the following properties :-
• Perfect 50:50 balance, i.e.. always 6 one's & 6 zero's
• There are never more than 4 consecutive one's or zero's. This minimises the low frequency
components in the code and allows fast settling times to be used for the receivers' data slicer.
• Minimum Hamming distance = 2, i.e.. each code is different from any other code by a minimum of 2
bits, thus all odd number of bit errors will always be detected.
• In general only 256 of 4096 (6.25%) possible codes are valid, i.e.. a 93.75 % probability of trapping a
byte error.
• Preamble and the Frame sync codes are not part of the symbol alphabet, a 'clash' signal will cause
immediate termination of the current decode followed by an attempt to lock to the new signal.
Check Sum
Since the receiver checks each symbol for integrity, a simple 8 bit check sum is used to test for overall
packet integrity. This is also coded into a 12 bit symbol prior to transmission.
Radiometrix Ltd, RPC
page 19
The RPC's Packet Decoder
Signal Decoding is in 4 stages :-
Search
Initially the RPC's decoder searches the radio noise on the RXD line for the 20kHz preamble signal.
The search is performed by a 16 times over-sampling detector which computes the spectral level of
20kHz in 240 samples of the RXD signal (750µs window).If the level exceeds a pre-set threshold the
decoder will attempt to decode a packet.
Lock-in
The same set of 240 samples are used to compute the phase of the incoming preamble and synchronise
the internal recovery clock to an accuracy of +/- 2µs. The recovery clock samples the mid point of each
incoming data bit and shifts the samples trough an 8 bit serial comparator. The comparator searches
the data on a bit by bit basis for the frame sync byte. While the search is in progress, the decode will
abort if the preamble fails to maintain a certain level of integrity. If the comparator finds the 'please
hold the line' code used during extended wake-up preamble a phase re-lock is triggered to ensure
accurate phase tracking until the actual packet arrives. When the frame sync is detected the decoder
attains full synchronisation and will move to the Decode state.
Decode
Data is now taken in 12 bits at a time (one symbol), decoded into the original byte and placed in the
receive buffer. The symbol decoder verifies each received symbol as valid (only 256 out of a possible
4096 are valid) and will immediately abort the decode on a symbol failure. The first byte contains the
byte count and is used to determine the end of message.
Check Sum
The last byte is the received check sum, this is verified against a locally generated sum of all the
received bytes in the packet. If it matches the packet is valid and RXR line will be pulled low to inform
the Host that a packet awaits uploading.
Notes on error handling
The RPC’s' decoder is deliberately non bit error tolerant, i.e.. no attempt is made to repair corrupt data
bits. All of the redundancy in the code is directed towards error checking. For an FM radio link using
short packet lengths, e.g. RPC + BiM , packets are either 100% or so grossly corrupt as to be
unrecoverable. By the same reasoning, the Host is not informed when the RPC decoder aborts a packet
decode since corrupt information is of little value. A packet acknowledge Time-Out and re-transmission
is the preferred strategy for error handling.
Radiometrix Ltd, RPC
page 20
APPENDIX - B
Example RPC driver subroutines for Arizona PIC16C73
figure 16: RPC to PIC -µC interface
Packet transfers to / from the RPC are best handled in the host by two subroutines :- OUT_BYTE &
IN_BYTE
Additionally LISTEN_BUS is called on completion of a packet transfer to the RPC to return the data
bus to inputs (default state).
;--------------------------------------------------------------------;
;
;
;
;
RPC DRIVERS
;--------------------------------------------------------------------
;
;
;
RPC
;
;
;
D7
D6
D5
D4
TXA
TXR
RXA
RXR
;
HOST PROCESSOR PIC16C73 or similar
EQU
06
;USE PORT B ON PIC
** Bit assignments for RPC PORT **
EQU
EQU
EQU
EQU
EQU
EQU
EQU
EQU
7
6
5
4
3
2
1
0
;Bi-Dir
;Bi-Dir
;Bi-Dir
;Bi-Dir
;INPUT
;OUTPUT
;OUTPUT
;INPUT ON RB0, CAN BE CONFIGURED AS AN INTERRUPT
RPC_DDR 86
;
;
;Data direction register for port B (RPC)
;This register is in BANK 1 of the register file
;--------------------------------------------------------------------
;
W
F
EQU
EQU
0
;Accumulator as Destination
;Register File as Destination
;INDirect File register
1
INDF EQU
00
Radiometrix Ltd, RPC
page 21
;SUBROUTINE IN_BYTE
;
;IN_BYTE
READ A BYTE FROM THE RPC INTO FILE POINTED TO BY FSR
;
;
;
;
;
;
W IS DESTROYED
NOTE THIS ROUTINE WILL HANG THE HOST UNTIL THE HOST
COMPLETES THE TRANSFER OF TWO NIBBLES
THIS SUBROUTINE CAN BE CONFIGURES TO RUN AS PART OF
ANINTERRUPT HANDLER IF THE :RXR LINE FROM THE RPC
IS USED TO TRIGGER A HOST INTERRUPT
:
;
;
IN_BYTE
BTFSC RPC,RXR
GOTO IN-BYTE
;WE GOT A RX REQUEST YET?
;NO , SO LOOP BACK AND WAIT
;
;
;
READ THE LS NIBBLE FROM THE RPC
BCF
RPC,RXA
;ACCEPT THE REQUEST (SET ACCEPT LOW)
;
AWAITDATA
BTFSS RPC,RXR
GOTO AWAITDATA
;HAS REQUEST GONE UP? data is present
;LOOP BACK TILL IT DOES
;
NOP
;TIME DELAY TO ENSURE DATA STABLE
;BEFORE READ
;
;
MOVF RPC,W
BSF
;READ THE LS NIBBLE FROM THE BUS
;TELL RPC WE GOT NIBBLE (ACCEPT = 1)
ANDLW B'11110000' ;JUST THE DATA
RPC,RXA
;
;
MOVWF INDF
SWAPF INDF
;SAVE LS NIBBLE IN TARGET FILE (VIA
;FSR)
;RIGHT JUSTIFY LS NIBBLE
;
;
NOW GET MS NIBBLE FROM THE RPC
;
;
INNIBBLE
BTFSC RPC,RXR
GOTO INNIBBLE
;WE GOT NEXT RX REQUEST YET ?
;NO , SO LOOP BACK AND WAIT
;
BCF RPC,RXA
;ACCEPT REQUEST (SET ACCEPT LOW)
;
AWAITD1
BTFSS RPC,RXR
GOTO AWAITD1
;HAS REQUEST GONE UP? data is present
;LOOP BACK TILL IT DOES
;
NOP
;TIME DELAY TO ENSURE DATA STABLE
;BEFORE READ
;
;
MOVF RPC,W
;READ THE MS NIBBLE FROM THE BUS
;TELL RPC WE GOT NIBBLE (ACCEPT=1)
BSF
RPC,RXA
ANDLW B'11110000' ;JUST THE DATA
;
IORWF INDF
;COMBINE MS NIBBLE WITH LS NIBBLE
;ALREADY
;IN THE FILE (VIA FSR)RETURN
;
;
;
;
A BYTE HAS BEEN READ FROM THE RPC INTO ADDRESS POINTED AT BY FSR
;--------------------------------------------------------------------
;
Radiometrix Ltd, RPC
page 22
;SUBROUTINE OUT_BYTE
;OUT_BYTE
WRITE A BYTE FROM FILE POINTED TO BY FSR TO RPC
;
;
;
;
;
;
W IS DESTROYED
NOTE THIS ROUTINE WILL HANG THE HOST UNTIL THE RPC
ACCEPTS THE TRANSFER OF TWO NIBBLES
WARNING
DETECTING A TXA FROM THE RPC.
THE CALLING ROUTINE MUST SET 4 DATA LINES
BACK TO I/P ON COMPLETION OF PACKET TRANSFER ;
(i.e. call LISTENBUS)
OUT_BYTE WILL SET THE DATA BUS TO DRIVE AFTER ;
;
;
;
OUT_BYTE
;
SWAPF INDF,W
;GET LS NIBBLE FROM FILE (VIA FSR) INTO
;BITS 4 to 7 of W
ANDLW B'11110000' ;JUST THE NIBBLE
IORLW B'00000010' ;SET TXR LOW, LEAVE RXA HIGH
MOVWF RPC
;SET TXR LOW, OUTPUT NIBBLE
;
WACCEPT
BTFSC RPC,TXA
GOTO WACCEPT
;WE GOT A TX ACCEPT BACK YET?
;NO, SO LOOP BACK AND WAIT
;
;WE GOT ACCEPTANCE SO IT'S OK TO DRIVE BUS
;
BSF
STATUS,RP0 ;SELECT PAGE 1
MOVLW B'00001001' ;DRIVE BUS
MOVWF RPC_DDR
BCF
STATUS,RP0 ;SELECT PAGE 0 BUS IS NOW DRIVING
;
BSF
RPC,TXR
;REMOVE REQUEST, DATA IS ON BUS
;HAS DATA BEEN READ?
WDUN
;
BTFSS RPC,TXA
GOTO WDUN
;WAIT TILL RPC REMOVES ACCEPT
;LS NIBBLE OF (FSR) IS SENT , NOW DO MS NIBBLE
;
MOVF INDF,W
;GET MS NIBBLE FROM FILE (VIA FSR)
;
ANDLW B'11110000' ;JUST THE MS NIBBLE
IORLW B'00000010' ;SET TXR LOW (BIT 2), RXA STAYS HIGH
MOVWF RPC
;OUTPUT NIBBLE + TXR LOW
;
WACCEPT1
BTFSC RPC,TXA
GOTO WACCEPT1
;WE GOT A TX ACCEPT BACK YET?
;NO, SO LOOP BACK AND WAIT
;
BSF
RPC,TXR
;REMOVE REQUEST, DATA IS ON BUS
;
WDUN1
BTFSS RPC,TXA
GOTO WDUN1
;HAS DATA BEEN READ?
;WAIT TILL RPC REMOVES ACCEPT
;
RETURN
;
;
BYTE IS SENT TO RPC
;--------------------------------------------------------------------
; SUBROUTINE - LISTEN_BUS , SET DATA BUS TO INPUT
;
LISTEN_BUS BSF STATUS,RP0
;SELECT PAGE 1
MOVLW B'11111001' ;BUS TO INPUT
MOVWF RPC_DDR
BCF
RETURN
STATUS,RP0 ;SELECT PAGE 0
;
BUS IS LISTENING TO RPC
;--------------------------------------------------------------------
Radiometrix Ltd, RPC
page 23
APPENDIX - C
Example RPC driver subroutines for Motorola 68HC11
figure 17: RPC to HC11 µ-C interface
Packet transfers to / from the RPC are best handled in the host by two subroutines :- OUT_BYTE &
IN_BYTE
Additionally LISTEN_BUS is called on completion of a packet transfer to the RPC to return the data
bus to inputs (default state).
*********************************************************************
*
* CPU REGISTER EQUATIONS
*
*********************************************************************
*
*This section contains a few of the necessary register equations used
*in the example subroutines.
PORTC
DDRC
EQU
EQU
$1003
$1007
;ADDRESS OF RPC PORT
;DATA DIRECTION REGISTER PORT-C
* Port-C7 = RX-accept OUTPUT
* Port-C6 = RX-request INPUT
* Port-C5 = TX-accept INPUT
* Port-C4 = TX-request OUTPUT
* Port-C3 = RPC data bit-3
* Port-C2 = RPC data bit-2
* Port-C1 = RPC data bit-1
* Port-C0 = RPC data bit-0
Radiometrix Ltd, RPC
page 24
**********************************************************************
* RANDOM ACCESS MEMORY
*
*
*********************************************************************
ORG
RAM
;RAM AREA DEFINITION
SAVE_1
SAVE_X
RMB
RMB
1
2
;TEMPORARILY SAVE LOCATION 1
;HOLDS FILES POINTER FOR IN_BYTE
**********************************************************************
* SUBROUTINE: IN_BYTE
*********************************************************************
*This subroutine is designed to be called by an interrupt handler to
*read a byte from the RPC into a file pointed at by X
*
*Note: The interrupt handler should load the X register with the file address
before calling this subroutine.
IN_BYTE
WAIT_RQ
IN_LP
CLR
SAVE_1
;CLEAR TEMPORARILY MEMORY LOCATION
LDAB #%10010000 ;SET CORRECT DATA DIRECTION i/p
STAB DDRC
LDAB PORTC
BITB #%01000000
BNE
LDAB PORTC
ANDB #%01111111 ;FORCE RX-ACCEPT TO GO LOW
STAB PORTC
LDAB PORTC
BITB #%01000000
;WAIT FOR RX-REQUEST TO GO LOW
;
WAIT_RQ
WAIT_RQ1
DAT_IN
;WAIT FOR RX-REQUEST TO GO HIGH
BEQ
LDAA PORTC
WAIT_RQ1
;READ IN DATA
ANDA #%00001111
LDAB PORTC
;FORCE ACCEPT HIGH
ORAB #%10000000
STAB PORTC
STAA SAVE_1
LDAB PORTC
BITB #%01000000
;SAVE NIBBLE TO TEMP LOCATION
;WAIT FOR RX-REQUEST TO GO LOW
WAIT_RQ2
IN_LP2
BNE
WAIT_RQ2
LDAB PORTC
ANDB #%01111111 ;FORCE RX-ACCEPT TO GO LOW
STAB PORTC
WAIT_RQ3
DAT_IN2
LDAB PORTC
;WAIT FOR RX-REQUEST TO GO HIGH
BITB #%01000000
BEQ
WAIT_RQ3
LDAA PORTC
ANDA #%00001111
ASLA
;READ IN DATA
ASLA
ASLA
ASLA
LDAB PORTC
ORAB #%10000000
STAB PORTC
ORAA SAVE_1
STAA SAVE_1
STAA 0,X
;FORCE ACCEPT HIGH
;PUT NIBBLES TOGETHER IN TEMP LOCATION
;SAVE DATA TO POINTER ADDRESS
READ_END
Radiometrix Ltd, RPC
page 25
**********************************************************************
* SUBROUTINE: OUT_BYTE
**********************************************************************
*This subroutine will output of one byte to the RPC. Register X
*should contain the address of the memory location of the byte to be *send.
*Note: that register X has to be pre-loaded before entering this *
subroutine.
OUT_BYTE
LDAA 0,X
;GET THE BYTE TO SEND TO RPC
ANDA #%00001111 ;PREPARE LEAST SIGNIFICANT NIBBLE
LDAB PORTC
ANDB #%11101111 ;FORCE TX-REQUEST LOW
STAB PORTC
LDAB PORTC
WAIT_ACC
BITB #%00100000 ;WAIT FOR TX ACCEPT TO GO LOW
BNE
LDAB #%10011111 ;CHANGE DATA DDRC TO OUTPUT
STAB DDRC ;TURN BUS DRIVE ON
ORAA #%10000000 ;MAKE SURE RXA IS HIGH
WAIT_ACC
STAA PORTC
LDAB PORTC
;OUTPUT DATA
ORAB #%00010000 ;FORCE TX-REQUEST HIGH
STAB PORTC
WAIT_REQ
LDAB PORTC
;WAIT FOR TX_ACCEPT TO GO HIGH
BITB #%00100000
BEQ
WAIT_REQ
LDAA 0,X
LSRA
;PREPARE MOST SIGNIFICANT NIBBLE
;BY SWAPPING THE LS- & MS-NIBBLE
LSRA
LSRA
LSRA
LDAB PORTC
ANDB #%11101111 ;FORCE TX-REQUEST LOW
STAB PORTC
WAIT_TXA1
WAIT_TXR1
LDAB PORTC
;WAIT FOR TX-ACCEPT TO GO LOW
BITB #%00100000
BNE
WAIT_TXA1
ORAA #%10000000
STAA PORTC
LDAB PORTC
;OUTPUT DATA
ORAB #%00010000 ;FORCE TX-REQUEST HIGH
STAB PORTC
LDAB PORTC
;WAIT FOR TX_ACCEPT TO GO HIGH
BITB #%00100000
BEQ
RTS
WAIT_TXR1
**********************************************************************
* SUBROUTINE: LISTEN TO BUS
*********************************************************************
*
*This will turn the RPC host to listen mode again and should
*be called when the whole packet has been sent to the RPC
*
LISTEN_BUS LDAA #%10010000 ;PUT PORT BACK TO LISTEN
STAA DDRC
RTS
*********************************************************************
Radiometrix Ltd, RPC
page 26
APPENDIX - D
The RPC as a control IC
Clock frequency
All timings within the RPC (except sleep) are determined by the clock frequency. The standard
frequency is 10.24MHz and all timings unless explicitly stated otherwise, assume this clock frequency.
fclk
The data rate =
bit / s
( i.e. 40kbit/s for Fclk=10.24MHz)
256
Clock accuracy
The RPC uses synchronous data transmission and requires an accurate reference clock. In the worst
case , max. preamble and packet length, the allowable bit rate timing error between transmitter and
receiver is 0.2 bits in 1000 bits, i.e. +/-200ppm total or +/-100ppm at each end.
256
BIT TIME =
Hz
i.e. 10.24 MHz crystal = 25.0µs PER BIT
fxtal
Accuracy, temp drifts MUST KEEP X-TAL +/- 100ppm of nominal
figure 18: RPC-000-SO & RPC-000-DIL outlines
Radiometrix Ltd, RPC
page 27
Radiometrix Ltd
4 Hartcran House
Gibbs Couch
Watford WD19 5EZ
ENGLAND
Tel: 020 8428 1220
Fax:020 8428 1221
Int ꢀ: +44 20 8428 1220
www.radiometrix.co.uk
info@radiometrix.co.uk
Copyright notice
This product data sheet is the original work and copyrighted property of Radiometrix Ltd.
Reproduction in whole or in part must give clear acknowledgement to the copyright owner.
Limitation of liability
The information furnished by Radiometrix Ltd is believed to be accurate and reliable.
Radiometrix Ltd reserves the right to make changes or improvements in the design,
specification or manufacture of its subassembly products without notice. Radiometrix Ltd does
not assume any liability arising from the application or use of any product or circuit described
herein, nor for any infringements of patents or other rights of third parties which may result
from the use of its products. This data sheet neither states nor implies warranty of any kind,
including fitness for any particular application. These radio devices may be subject to radio
interference and may not function as intended if interference is present. We do NOT recommend
their use for life critical applications.
Radio and EMC regulations
The Intrastat commodity code for all our modules is: 8542 4090.
The purchaser of Radiometrix subassemblies must satisfy all relevant EMC and other
regulations applicable to their finished products.
R&TTE Directive
After 7 April 2001 the manufacturer can only place finished product on the market under the
provisions of the R&TTE Directive. Equipment within the scope of the R&TTE Directive may
demonstrate compliance to the essential requirements specified in Article 3 of the Directive, as
appropriate to the particular equipment. Further details are available on
Radiocommunications
Agency
(RA)
web
site:
http://www.radio.gov.uk/topics/conformity/conform-index.htm
The Library and Information Service
The Radiocommunications Agency
Wyndham House, 189 Marsh Wall
London E14 9SX
United Kingdom
Tel: +44 (0)20 7211 0502 or 0505
Fax: +44 (0)20 7211 0507
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