AN665

DS00665A-page 10

ã 1997 Microchip Technology Inc.

00181

002F 0C0F

00182

movlw

.15

0030 0032

00183

movwf

TIMELO

0031

00184 SBitT2

0031 02F2

00185

decfsz

TIMELO,F

; 45us loop (data stable)

0032 0A31

00186

goto

SBitT2

00187

0033 0516

00188

bsf

GPIOTEMP,PCCLK

; clk rise

0034 0216

00189

movf

GPIOTEMP,W

0035 0006

00190

tris

GPIO

0036 0800

00191

retlw

0

00192

00193 ;**********************************************************************

00194 ;*

SendKEY

00195 ;*

sends a scan code to the PC

00196 ;*

00197 ;*

Input Variables:

00198 ;*

W

00199 ;*

Output Variables:

00200 ;*

none

00201 ;**********************************************************************

00202 ;

0037

00203 SendKEY

0037 0034

00204

movwf

AUX

; temp storage

00205

00206 ; wait PC ready

0038

00207 SendW

0038 0706

00208

btfss

GPIO,PCCLK

; test PCCLK

0039 0A38

00209

goto

SendW

; loop until HIGH

00210

00211 ; PC request ?

00212 ;

btfss

DATA

; PC pull down Data?

00213 ;

goto

RecKEY

; go receive first

00214

00215 ; send start bit

003A 0403

00216

bcf

STATUS,C

003B 0922

00217

call

SendBit

00218

00219 ; than shift out 8 bit LSB first

003C 0C08

00220

movlw

.8

003D 002F

00221

movwf

BITCOUNT

003E 0073

00222

clrf

PARITY

00223

003F

00224 SBitL

003F 0334

00225

rrf

AUX,F

; next bit

0040 0603

00226

btfsc

STATUS,C

0041 02B3

00227

incf

PARITY,F

; count parity

0042 0922

00228

call

SendBit

0043 02EF

00229

decfsz

BITCOUNT,F

0044 0A3F

00230

goto

SBitL

; loop for 8 bit

00231

0045 02B3

00232

incf

PARITY,F

; parity odd

0046 0333

00233

rrf

PARITY,F

; send parity Bit

0047 0922

00234

call

SendBit

00235

0048 0503

00236

bsf

STATUS,C

0049 0A22

00237

goto

SendBit

; send stop bit (high = released)

00238

00239

00240 ;**********************************************************************

00241 ;*

Receive

00242 ;*

receives first 64 bit transmitted by an HCS300 encoder

00243 ;*

simplified to operate with 400us PWM only

00244 ;*

00245 ;*

Input Variables:

00246 ;*

none