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The address of this routine is found in the initial channel information table.
This important subroutine returns the code of the last key to have been pressed, but note that CAPS LOCK, the changing of the mode and the colour control parameters are handled within the subroutine.
A Code of the last key pressed
F Carry flag set if a key was pressed
KEY_INPUT 04264 BIT 3,(IY+2) Copy the edit-line or the INPUT-line to the screen if the mode has changed (bit 3 of TV-FLAG set).
04271 AND A Return with both carry and zero flags reset if no new key has been pressed (bit 5 of FLAGS reset).
04272 BIT 5,(IY+1)
04276 RET Z
04277 LD A,(23560) Otherwise fetch the code (LAST-K) and signal that it has been taken (reset bit 5 of FLAGS).
04280 RES 5,(IY+1)
04284 PUSH AF Save the code temporarily.
04285 BIT 5,(IY+2) Clear the lower part of the display if necessary (bit 5 of TV-FLAG set), e.g. after 'scroll?'.
04292 POP AF Fetch the code.
04293 CP " " Accept all characters and token codes.
04295 JR NC,KEY_DONE_2
04297 CP 16 Jump forward with most of the control character codes.
04301 CP 6 Jump forward with the 'mode' codes and the CAPS LOCK code.
04303 JR NC,KEY_M_CL
Now deal with the FLASH, BRIGHT and INVERSE codes.
04305 LD B,A Save the code.
04306 AND 1 Keep only bit 0.
04308 LD C,A C holds 0 (=OFF) or 1 (=ON).
04309 LD A,B Fetch the code.
04310 RRA Rotate it once (losing bit 0).
04311 ADD A,18 Increase it by 18 giving 18 for FLASH, 19 for BRIGHT, and 20 for INVERSE.
The CAPS LOCK code and the mode codes are dealt with 'locally'.
KEY_M_CL 04315 JR NZ,KEY_MODE Jump forward with 'mode' codes.
04317 LD HL,23658 This is FLAGS2.
04320 LD A,8 Flip bit 3 of FLAGS2. This is the CAPS LOCK flag.
04322 XOR (HL)
04323 LD (HL),A
04324 JR KEY_FLAG Jump forward.
KEY_MODE 04326 CP 14 Check the lower limit.
04328 RET C
04329 SUB 13 Reduce the range.
04331 LD HL,23617 This is MODE.
04334 CP (HL) Has it been changed?
04335 LD (HL),A Enter the new 'mode' code.
04336 JR NZ,KEY_FLAG Jump if it has changed; otherwise make it 'L mode'.
04338 LD (HL),0
KEY_FLAG 04340 SET 3,(IY+2) Signal 'the mode might have changed' (set bit 3 of TV-FLAG).
04344 CP A Reset the carry flag and return.
04345 RET
The control key codes (apart from FLASH, BRIGHT and INVERSE) are manipulated.
KEY_CONTR 04346 LD B,A Save the code.
04347 AND 7 Make the C register hold the parameter (0 to 7).
04349 LD C,A
04350 LD A,16 A now holds the INK code.
04352 BIT 3,B But if the code was an 'unshifted' code then make A hold the PAPER code.
04356 INC A
The parameter is saved in K-DATA and the channel address changed from KEY_INPUT to KEY_NEXT.
KEY_DATA 04357 LD (IY-45),C Save the parameter at K-DATA.
04360 LD DE,4365 This is KEY_NEXT.
04363 JR KEY_CHAN Jump forward.
Note: on the first pass entering at KEY_INPUT the A register is returned holding a 'control code' and then on the next pass, entering at KEY_NEXT, it is the parameter that is returned.
KEY_NEXT 04365 LD A,(23565) Fetch the parameter (K-DATA).
04368 LD DE,4264 This is KEY_INPUT.
Now set the input address in the first channel area.
KEY_CHAN 04371 LD HL,(23631) Fetch the channel address (CHANS).
04374 INC HL
04375 INC HL
04376 LD (HL),E Now set the input address.
04377 INC HL
04378 LD (HL),D
Finally exit with the required code in the A register.
KEY_DONE_2 04379 SCF Show a code has been found and return.
04380 RET
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