z80:Input Routines

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The main source of user input will be through the keypad, so almost every input routine will require use of a GetKey function.

Note: This page will need to have routines for actual user input aside from GetKey routines.

GetKey

This is essentially like several of the OS routines. If OS interrupts are read, you can also read from address 8445h. But if you really want a custom routine:

   ;===============================================================
   GetKey:
   ;===============================================================
   ;Outputs:
   ;     A is a value from 0 to 56 that is the keypress
   ;    HL is not modified
   ;    BC is not modified
   ;Destroys:
   ;    D
   ;    E is destroyed if no keys are pressed, else it is also the keypress
   ;===============================================================
        ld de,$7FFF
   KeyLoop:
        rlc d
        ld a,d
        out (1),a
        sub 7Fh
        ret z
        ld a,e
        add a,8
        ld e,a
        in a,(1)
        inc a
        jr z,KeyLoop
        dec a
          inc e
          rra
          jr c,$-2
        ld a,e
        ret

ScanAllKeys

This routine requires 7 bytes of RAM pointed to by HL. This will return the value of all the key groups, stored in each of the bytes:

   ScanAllKeys:
   ;Inputs:
   ;     HL points to the 7 bytes to output the result to
   ;Notes:
   ;     There is not enough delay for 15MHz
        ld bc,0701h
        ld a,$FE      ;test the keys
   KeyUpdateLoop:
        out (1),a
        rlca
        nop
        ini
        jr nz,KeyUpdateLoop
        ret