Texas Instruments TI-83 Plus Manual page 107

Chapter 2: TI-83 Plus Specific Information
Example one:
The following routine is called to do a spot check of the link port for activity for a
single byte of data being sent.
– If no activity is detected or any error occurs during communication, then Z = 0 is
returned.
If activity is detected, then the signal is debounced to make sure it is not random
–
noise.
– The byte is then read and returned in the ACC with Z = 1.
haveIOcmd:
;
dblp1:
;
;
EndexIO:
;
linkfail:
NoIO:
TI-83 Plus Developer Guide
IN A,(bport)
AND D0D1_bits
CP D0D1_bits
JR Z,..noio
DI
LD HL,ioData
LD (HL),A
LD BC,15
IN A,(bport)
AND D0D1_bits
CP (HL)
JR NZ, noIO
DEC BC
LD A, C
OR B
JR NZ, dblp1
AppOnErr Linkfail
SET indicOnly,(IY+indicFlags) ; no key scan
B_CALL RecAByteIO
RES indicOnly,(IY+indicFlags) ; read the byte
LD (ioData),A
AppOffErr
LD A,D0HD1H
OUT (bport),A
LD A,(ioData)
CP A
EI
RET
LD A,D0HD1H
OUT (bport),A
OR 1
EI
RET
; poll the port
; jump if no activity
; for speed
; save code
; debounce counter
; poll again
; still the same data?
; no, failed debounce
; dec counter
; jump if debounce not done
; set error handler
; save data
; remove error handler
; reset B-port
; get data byte
; Z = 1 for successful
; reset B-port
; Z = 0 for fail
Third Release May 28, 2002
97