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You can find the rom listing at http://www.wearmouth.demon.co.uk/zx81.htm
Interesting bits for you below.
cya, Andrew...
; -----------------------
; THE 'INKEY$' EVALUATION
; -----------------------
CALL L02BB ; routine KEYBOARD
LD B,H ;
LD C,L ;
LD D,C ;
INC D ;
CALL NZ,L07BD ; routine DECODE
LD A,D ;
ADC A,D ;
LD B,D ;
LD C,A ;
EX DE,HL ;
JR L0FED ; forward to S-STRING
; THE 'INKEY$' EVALUATION
; -----------------------
CALL L02BB ; routine KEYBOARD
LD B,H ;
LD C,L ;
LD D,C ;
INC D ;
CALL NZ,L07BD ; routine DECODE
LD A,D ;
ADC A,D ;
LD B,D ;
LD C,A ;
EX DE,HL ;
JR L0FED ; forward to S-STRING
; ----------------------------------
; THE 'KEYBOARD SCANNING' SUBROUTINE
; ----------------------------------
; The keyboard is read during the vertical sync interval while no video is
; being displayed. Reading a port with address bit 0 low i.e. $FE starts the
; vertical sync pulse.
;; KEYBOARD
L02BB: LD HL,$FFFF ; (16) prepare a buffer to take key.
...
; THE 'KEYBOARD SCANNING' SUBROUTINE
; ----------------------------------
; The keyboard is read during the vertical sync interval while no video is
; being displayed. Reading a port with address bit 0 low i.e. $FE starts the
; vertical sync pulse.
;; KEYBOARD
L02BB: LD HL,$FFFF ; (16) prepare a buffer to take key.
...
; -------------------------------
; THE 'KEYBOARD DECODING' SECTION
; -------------------------------
; The decoded key value is in E and HL points to the position in the
; key table. D contains zero.
;; K-DECODE
L04DF: LD A,($4006) ; Fetch value of system variable MODE
....
; THE 'KEYBOARD DECODING' SECTION
; -------------------------------
; The decoded key value is in E and HL points to the position in the
; key table. D contains zero.
;; K-DECODE
L04DF: LD A,($4006) ; Fetch value of system variable MODE
....
-----Original Message-----I am working on a ZX81 machine code program.
From: zx81forever [mailto:zx81forever@...]
Sent: Saturday, 10 January 2004 4:46 PM
To: zxgate@yahoogroups.com
Subject: [zxgate] ZX81 Machine Code ???
I have a question. I believe the answer may
have appeared in SYNC Magazine (Vol.3 No.6,
featuring "Machine Language:ROM Calls" ???)
but my copy has been misplaced.
My question: how do you determine which key
has been pressed? I need to know the CODE
value of the key pressed.
If I remember correctly, there is a ROM call,
followed by the placing of register BC in HL,
followed by another ROM call.
If anyone can post the exact details, or scan
the "ROM Calls" article out of SYNC (that'll
be a very big help), I would appreciate it.
Thank you,
zx81forever@...
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