; ; unsigned char kbhit (void); ; ; The method to detect a pressed key is based on the documentation in ; "Section 3 Programmed Key Functions" in "The Challenger Character Graphics ; Reference Manual" ; We only want to return true for characters that can be returned by cgetc(), ; but not for keys like or . Therefore a special handling is ; needed for the first row. This is implemented by a bit mask that is stored ; in tmp1 and that is set to zero after the first round. ; .constructor initkbhit .export _kbhit .include "osic1p.inc" .include "extzp.inc" .include "zeropage.inc" ; Internal state that needs to be preserved across calls. .segment "EXTZP" : zeropage LASTSCAN: .res 1 ; Result of previous keyboard scan DBNCCNT: .res 1 ; Debounce counter KBDTMP: .res 1 ; Temporary values CTRLSHIFT: .res 1 ; State of CTRL and SHIFT keys ; Initialize one-character buffer that is filled by kbhit() .segment "ONCE" initkbhit: lda #$00 sta CHARBUF ; No character in buffer initially sta LASTSCAN ; Initialize keyboard state sta DBNCCNT sta KBDTMP sta CTRLSHIFT rts ; Routine to get character from keyboard and return it in A. ; Based on the OSI ROM routine at $FD00 but uses different ; storage locations to avoid corrupting CC65 run-time code. _kbhit: lda CHARBUF ; Check for previously saved character beq LFD05 ldx #$00 ; High byte of return is always zero rts ; A contains non-zero character code meaning true LFD05: lda #$80 ; Bit mask for initial keyboard row LFD06: jsr LFCBE ; Write keyboard row jsr LFCC6 ; Read keyboard column bne LFD13 ; Branch if a key in this column was pressed lsr a ; Otherwise shift mask to next row bne LFD06 ; If not done yet, check next row beq LFD3A ; Branch if last row reached and no key pressed LFD13: lsr a ; Have a key press. Shift LSB into carry bcc LFD1F ; Branch if no key pressed in column 0 txa ; Key pressed in row zero. Get the column data and #$20 ; Mask only the bit for as it is the only key in row zero that returns key press beq LFD3A ; Branch if was not the key lda #$1B ; Set character to bne LFD50 ; Do more processing LFD1F: jsr LFE86 ; Shift to find bit that is set (in Y) tya ; Get bit sta KBDTMP ; Save it asl a ; Multiply by 7 by shifting left three times (X8)... asl a asl a sec ; ...then subtracting one sbc KBDTMP sta KBDTMP ; Save value*7 for later lookup in table txa ; Get the keyboard column lsr a ; Shift out bit zero (only key there is ) asl a ; And shift back jsr LFE86 ; Shift to find bit that is set (in Y) beq LFD47 ; Branch if no keys pressed lda #$00 LFD3A: sta CTRLSHIFT ; Save state of and shift keys LFD3D: sta LASTSCAN lda #$02 ; Count used for key debouncing sta DBNCCNT ldx #$00 ; High byte of return is always zero lda #$00 ; Return false rts LFD47: clc tya ; Get bit number of pressed key adc KBDTMP ; Add previously calculated offset for keyboard row*7 tay lda LFF3B,y ; Read ASCII code for key from table LFD50: cmp LASTSCAN ; Debounce - same as last key scan? bne LFD3D ; If not, try again dec DBNCCNT ; Decrement debounce counter beq LFD5F ; Branch if done debouncing jsr LFCDF ; Wait for short delay to debounce keyboard beq _kbhit ; Go back and scan keyboard. LFD5F: ldx #$64 ; Was key down? cmp CTRLSHIFT bne LFD68 ; Branch if not ldx #$0F LFD68: stx DBNCCNT sta CTRLSHIFT cmp #$21 bmi LFDD0 ; Done, return key cmp #$5F beq LFDD0 ; Done, return key lda #$01 jsr LFCBE ; Write keyboard row jsr LFCCF ; Read keyboard column sta KBDTMP tax and #$06 bne LFDA2 bit LASTSCAN bvc LFDBB txa eor #$01 and #$01 beq LFDBB lda #$20 bit KBDTMP bvc LFDC3 lda #$C0 bne LFDC3 LFDA2: bit LASTSCAN bvc LFDAA txa beq LFDBB LFDAA: ldy LASTSCAN cpy #$31 bcc LFDB9 cpy #$3C bcs LFDB9 lda #$F0 bne LFDBB LFDB9: lda #$10 LFDBB: bit KBDTMP bvc LFDC3 clc adc #$C0 LFDC3: clc adc LASTSCAN and #$7F bit KBDTMP bpl LFDD0 ora #$80 LFDD0: sta KBDTMP ; Save pressed key and return in A sta CHARBUF rts ; Write keyboard row with value in A. ; Invert the bits before writing. ; Returns original value of A. LFCBE: eor #$FF sta KBD eor #$FF rts ; Read keyboard column and return in X. ; Sets Z flag if no keys were pressed. ; Saves current value of A. LFCC6: pha ; Save A jsr LFCCF ; Read keyboard column tax ; Save in X pla ; Restore A dex ; Decrement and then increment to inx ; preserve value of X but set flags rts ; Read keyboard column. ; Invert the bits (pressed key(s) will show up as ones). LFCCF: lda KBD ; Read keyboard hardware eor #$FF ; Invert the bits rts ; Short fixed delay routine. LFCDF: ldy #$10 LFCE1: ldx #$40 LFCE3: dex bne LFCE3 dey bne LFCE1 rts ; Shift A left until we find a 1 in the most significant bit. ; Return the bit number in Y. LFE86: ldy #$08 LFE88: dey asl a bcc LFE88 rts ; Lookup table of keyboard keys for each scan row. LFF3B: .byte $BD .byte 'P', ';', '/', ' ', 'Z', 'A', 'Q' .byte ',', 'M', 'N', 'B', 'V', 'C', 'X' .byte 'K', 'J', 'H', 'G', 'F', 'D', 'S' .byte 'I', 'U', 'Y', 'T', 'R', 'E', 'W' .byte $00, $00, $0D, $0A, 'O', 'L', '.' .byte $00, '_', '-', ':', '0', '9', '8' .byte '7', '6', '5', '4', '3', '2', '1'