ST72T251G2B6 [STMICROELECTRONICS]

8-BIT MCU WITH 4 TO 8K ROM/OTP/EPROM, 256 BYTES RAM, ADC, WDG, SPI, I2C AND 2 TIMERS; 8位MCU 4〜 8K ROM / OTP / EPROM ， 256字节RAM ， ADC ， WDG ， SPI ， I2C和2定时器


型号：	ST72T251G2B6
厂家：	ST
描述：	8-BIT MCU WITH 4 TO 8K ROM/OTP/EPROM, 256 BYTES RAM, ADC, WDG, SPI, I2C AND 2 TIMERS 8位MCU 4〜 8K ROM / OTP / EPROM ， 256字节RAM ， ADC ， WDG ， SPI ， I2C和2定时器微控制器和处理器外围集成电路光电二极管可编程只读存储器电动程控只读存储器时钟
文件：	总11页 (文件大小：70K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

APPLICATION NOTE

ST7 KEYPAD DECODING TECHNIQUES, IMPLEMENTING

WAKE-UP ON KEYSTROKE

by Microcontroller Division Application Team

INTRODUCTION

The goal of this application note is to present an example of the use of the HALT mode.

In this application, the MCU (here a ST72251) is waked up by an external interrupt caused by

someone pressed a key on the 4x4 matrixed keypad.

1 ST7 / KEYBOARD INTERFACE

Rows are connected to inputs with pull-up and interrupts (Port C). Columns are connected to

Port A configured as output. The result of the interrupt (the value of the pressed key) is sent on

LEDS (Port B) and stored into the X register. In our configuration, we have to add 4 pull-up re-

sistors on Port A (from PA0 to PA3) to be able to apply a high level on the corresponding pads.

Figure 1. ST7 / keypad interface set-up

4x100k

8x560

PC0

PC1

PC2

PC3

ST7

PA0

PA1

PA2

PA3

GND

AN980/1098

1/10

ST72251 CONFIGURATION

2 ST72251 CONFIGURATION

The application has been validated with a ST72251. Its configuration is described in this part.

Refer to your datasheet for more details.

2.1 I/O CONTROL

Rows are connected to pins configured as inputs (Port C as input with pull up and interrupts).

Columns are connected to pins configured as outputs (Port A).

External interrupts are caused by a low level applied to a pin of Port C (caused by a key

pressed), they wake up the MCU which was in HALT mode.

Port B is configured as outputs to send the value of the pressed key on LEDS.

Please, refer to the Data Book to configure pins properly.

2.2 MISCELLANEOUS REGISTER

Bits 7 and 6 have to be set to configure events correctly: the external interrupt (EI1) has here

to be caused by a falling edge only.

Please, refer to the datasheet for more details.

2.3 HALT MODE

The HALT instruction places the ST72251 in its lowest power consumption mode. The core

and all peripherals are frozen. In this mode, the internal oscillator is turned off, causing all in-

ternal processing to be halted. The data remain unchanged. During the HALT mode, external

interrupts are still enabled. The MCU stays in this state until an external interrupt or a reset oc-

curs. Then the internal oscillator is restarted and the core waits for 4096 CPU clock cycles

(512 µs for a f

= 8MHz) before running the external interrupt subroutine. Then the MCU

CPU

comes back to the main program (in our application to the HALT state).

Please, refer to the datasheet for more details.

3 EXTERNAL INTERRUPTS

The MCU is in HALT mode. When a key is pressed, a low level is applied to the pin corre-

sponding to the row the key belongs (pins configured as inputs with pull-up). It’s a falling edge

applied to a pin of Port C which creates an external interrupt (EI1) and wakes up the MCU. The

MCU executes then the external interrupt subroutine (decoding the pressed key) and comes

back to its previous state (HALT state in the main program).

2/10

KEYPAD

4 KEYPAD

The keypad used is a 4x4 matrixed keypad. Rows are connected to pins configured as inputs

with pull-up. So the initial state of these pins are a high level (1). When a key is pressed, a low

level is applied to the corresponding pin. For this reason, the keypad is coded as follows:

Table 1. Key values

row

column

value

row

column

value

KEY

value

0x0E

0x0D

0x0E

0x0D

0x0B

0x07

0x0E

0x0D

0x0B

0x07

0x0B

0x07

0x0E

0x0D

0x0B

0x07

0x0E

0x0D

0x0B

0x07

PC0

PC1

PC2

PC3

PA1

PA0

PA2

PA3

You have to press the chosen key at least 0.5 to 1 second depending on which key you

choose (table read from keypad_top to keypad). The faster the key is read into the table, the

faster it will be decoded and the faster the result will be sent on LEDS.

3/10

KEYPAD

The keypad code is in the file constant.asm as follows:

.keypad

DC.B

$0E,$0E,$1

$0E,$0D,$2

$0E,$0B,$3

$0E,$07,$F

$0D,$0E,$4

$0D,$0D,$5

$0D,$0B,$6

$0D,$07,$E

$0B,$0E,$7

$0B,$0D,$8

$0B,$0B,$9

$0B,$07,$D

$07,$0E,$A

$07,$0D,$0

$07,$0B,$B

$07,$07,$C

;PC0PA0

;PC0PA1

;PC0PA2

;PC0PA3

;PC1PA0

;PC1PA1

;PC1PA2

;PC1PA3

;PC2PA0

;PC2PA1

;PC2PA2

;PC2PA3

;PC3PA0

;PC3PA1

;PC3PA2

;PC3PA3

keypad_top

4/10

FLOWCHARTS

5 FLOWCHARTS

Figure 2. Flowchart: Main program

Initializations

infinite

loop

HALT

Figure 3. Flowchart: external interrupt (EI1)

X = 48 (3x16 coded values)

one column activated

(PA0...PA3)

Is there a low level on the

intersection of the stored

row and column?

store into X

next column

value

yes

corresponding value of the pressed key

stored into A, X and sent on LEDS

EXIT

5/10

SOFTWARE

6 SOFTWARE

The assembly code given below is guidance only. The complete software with all the files can

be found in the software library.

st7/

;thefirstlineisreserved

;forspecifyingtheinstructionset

;ofthetargetprocessor

;************************************************************************

;TITLE:

WAKE.ASM

;AUTHOR:

PPGMicrocontrollerApplicationsTeam

Mainprogram(useoftheHaltmodefordecoding

akeypad).

;DESCRIPTION:

;

;************************************************************************

TITLE "WAKE.ASM"

;thistitlewillappearoneach

;pageofthelistingfile

MOTOROLA

;thisdirectiveforcestheMotorola

;formatfortheassembly(default)

#INCLUDE“st72251.inc”;includest72251registersandmemorymappingfile

#INCLUDE“constant.inc”;includegeneralconstantsfile

;***********************************************************************

;

Variables,constantsdefinedandreferencedlocally

Youcandefineyourownvaluesforalocalreferencehere

;***********************************************************************

;************************************************************************

;

Publicroutines(definedhere)

;************************************************************************

WORDS

segment'rom'

.Init

LD A,#$80

LD MISCR,A

;interruptsarecausedbyfallingedge(onPortC).

LD A,#$0F

LD PBDDR,A

LD PBOR,A

;PB0toPB3configuresasoutputs(LEDS).

;PA0toPA3configuredasoutputs.

LD PADDR,A

CLR PAOR

CLR PADR

LD A,#$0F

6/10

SOFTWARE

LD PCOR,A

CLR PCDDR

CLR PCDR

;PCOtoPC3configuredasinputwithpull-upandinterrupt.

RET

.delay_45

LD A,#200

loop2 LD X,#$FF

loop1 DEC X

JRNE loop1

DEC A

JRNE loop2

RET

;**********************************************************

Programcode

;

;**********************************************************

.main

CALL Init

loop

HALT

;MCUputinlowestpowermode.

JRA loop

;Infiniteloop,waitaninterruptoccurs.

;*****************************************************************

;Thissetofinstructionsusessimpleassemblymnemoniques.

;Wecannoticethatthelooplabelisdefinedonlylocally(nodot

;infrontofit)soitcannotbeseenbyothersmoduleslinked

;withthisfile.

;*****************************************************************

;

********************************************

* INTERRUPTSUB-ROUTINESLIBRARYSECTION *

********************************************

.dummy iret

.sw_rt iret ;Emptysubroutine.Gobacktomain(iretinstruction)

.ext0_rtiret

.ext1_rt

LD X,#48

;SizeofthetablestoredinX.

;3x16codedvalues.

begin

7/10

SOFTWARE

LD A,PADR

OR A,#$0F

;Outputsforcedto1(initialvalue).

AND A,({keypad+1},X)

LD PADR,A

;onecolumnofthetestedrowisactivated.

PUSH X

CALL delay_45

POP X

;wait45ms(debouncingprocedure).

LD A,PCDR

AND A,#$0F

CP A,(keypad,X)

JREQ OK

;valueofPortCstoredintoA.

;searchofthelowlevelcolumnaftercolumn.

;ifkeyfound->OK.

DEC X

;3timestohavenextvalueofthecolumn.

;doitagaintoreadthewholetable(matrix).

JRPL begin

JRA exit

LD A,({keypad+2},X)

LD X,A

;StorethekeyvalueinA.

;CopyitintoX.

LD PBDR,X

;OutputtheresultonLEDS.

exit

CLR PADR

CLR PCDR

iret

.spi_rt iret

.tima_rtiret

.timb_rtiret

.i2c_rt iret

segment'vectit'

;*******************************************************************

;Thislastsegmentshouldalwaysbethereinyourownprograms.

;Itdefinestheinterruptvectoradressesandtheinterruptroutines'labels

;consideringthemicrocontrolleryouareusing.

;RefertotheMCU'sdatasheettoseethenumberofinterruptvector

;usedandtheiraddresses.

;RemindthatthisexampleismadeforaST72251basedapplication.

;*******************************************************************

8/10

SOFTWARE

;*******************************************************************

;Eachinterruptvectorusestwoaddressesinrom,that'swhatthedirective

;DC.Wmeans.Itsays"reserveawordlocation(.W)inrom(DC)andcode

;theroutine'slabelinthosetwoaddresses.

;Yet,whenaninterruptoccurs,forexamplefromthetimerB,timerb'sroutine

;address(timb_rt)willbeloadedinthePCandtheprogramwilljumptothis

;labelifallowed.Itwillexecutethisroutineandthenwillgobacktothemain

;program(seeinterruptchapterinthedatasheetforamoreprecisedescription

;ofhowtohandleinterruptsinST72micros).

;*******************************************************************

DC.W dummy

;FFE0-FFE1hlocation

;FFE2-FFE3hlocation

.i2c_it

DC.W i2c_rt ;FFE4-FFE5hlocation

DC.W dummy

;FFE6-FFE7hlocation

;FFE8-FFE9hlocation

;FFEA-FFEBhlocation

;FFEC-FFEDhlocation

.timb_it

DC.W timb_rt;FFEE-FFEFhlocation

DC.W dummy ;FFF0-FFF1hlocation

.tima_it

.spi_it

DC.W tima_rt;FFF2-FFF3hlocation

DC.W spi_rt ;FFF4-FFF5hlocation

DC.W dummy

;FFF6-FFF7hlocation

.ext1_it

.ext0_it

.softit

.reset

DC.W ext1_rt;FFF8-FFF9hlocation

DC.W ext0_rt;FFFA-FFFBhlocation

DC.W sw_rt

DC.W main

;FFFC-FFFDhlocation

;FFFE-FFFFhlocation

;Thislastlinereferstothefirstline.

;Itusedbythecompiler/linkertodeterminecodezone

END;BeawareofthefactthattheENDdirectiveshouldnot

;standontheleftofthepagelikethelabels'snames.

9/10

SOFTWARE

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10/10

This datasheet has been download from:

www.datasheetcatalog.com

Datasheets for electronics components.

ST72T251G2B6 [STMICROELECTRONICS]

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