Z-80 PIO PS/2 Keyboard interface
This project goal is to create a simple PS/2 keyboard interface using the Z-80 PIO.
z80_pio_ps2.pdfSchematic of the Z-80 PIO interface with the PS/2 Keyboard
Above: PS/2 Keyboard serial data packet diagram.
A simple overview of the PS/2 Keyboard, for both reading and sending data the Keyboard sends out the Clock signal. The serial interface uses an open collector system. The host(Computer) controls the keyboards sending or receiving by holding the Clock or Data line low. The keyboard clock is between 10 kHz and 16.7 kHz, about on clock every 0.0001 ms, vs say the Z80 at 4Mhz is 0.0000002.5 ms
Data = high, Clock = high: Idle state.
Data = high, Clock = low: Communication Inhibited.
Data = low, Clock = high: Host Request-to-Send
Keyboard to computer, to Inhibit communication at any time by pulling the Clock line low for at least 100 microseconds. If this is done during the sending of the data packet, the last data packet will be resent on release of the Clock line.
/* test PS/2 program */
#include "Hyundai_256x128.h"#include "Z80_IO.h"#include "ps2_keyboard.h"#include <z80.h>#include <stdlib.h>#include <ctype.h>
extern void isr_pio_0_a(void);extern void isr_pio_0_b(void);extern int vid_pio_0_a;extern int vid_pio_0_b;
void int2ascii(unsigned int cx, char *ptr );void system_init(void);void Button_press(void);char kbd_char_bf(void);
int pio_int_a = 0, pio_int_b = 0, int_38 = 0, add_isr = 0 , kbd_tmp = 0;char kbd_bit=0;
char kbd_buffer[16], kbd_char, kbd_up = 0, kbd_clt = 0, kbd_last_char = 0, kbd_ptr = 0 , kbd = 0;
char shift_r = 0, shift_l = 0, shift_active = 0;
void delay(int j){int i;for(i=0; i<j; i++);}
int main(){
char a, data[10], data2[11]; int x, int_38_count = 0, port_a = 0, port_b = 0, couter_1 = 0, pio_a_couter = 0, pio_b_couter = 0, alt, k[4] ;
data2[10] = 0;
system_init();
LCD_set_cursor(0 , 0);LCD_print("Interrupt test\0");z80_outp( Z80_PIO_A_CTL, Z80_PIO_DI);z80_outp( Z80_PIO_B_CTL, Z80_PIO_DI);
/*__asm ld hl, _vid_pio_0_a ld (_add_isr),hl im 1 ei
__endasm;
*///z80_outp( Z80_PIO_A_CTL, Z80_PIO_EI);
// set up Z80 PIO vector interrupts
__asm di ld hl, _vid_pio_0_a ld a, l out (0x02), a ld hl, _vid_pio_0_b ld a, l out (0x03), a //ld a, h //ld i, a im 2 ei__endasm;
for(x=0;x<76;x++){ps2_keyboard_state[x] = 0;}
LCD_clear();LCD_set_cursor(0 , 0);LCD_print("PS/2 Keyboard test\0");kbd_tmp = 0;pio_int_b = 0;kbd_bit = 0;alt = 0;port_b = z80_inp( Z80_PIO_B ); //Z80 PIO port B;z80_outp( Z80_PIO_B, 0x1f);__asm di__endasm;z80_outp( Z80_PIO_B_CTL, Z80_PIO_EI | Z80_PIO_EI_MF | Z80_PIO_EI_LOW |Z80_PIO_EI_AND ); // interrupt with mask 0x97z80_outp( Z80_PIO_B_CTL, 0x7f); // monitor port bit 2 0x3f__asm ei__endasm;
delay(100);
z80_outp( Z80_PIO_B, 0x3f);
while( port_b != 0xcc){
a = kbd_char_bf();
if( a != 0 ){ LCD_set_cursor(0 , 1); LCD_print( "Keyboard =\0"); int2ascii( kbd_last_char, data); LCD_print( data ); int2ascii( kbd, data); LCD_print( data ); LCD_set_cursor(0 , 2); LCD_print( "Keyboard buffer =\0"); int2ascii( kbd_ptr, data); LCD_print( data );kbd_last_char = kbd; LCD_set_cursor(0 , 3); LCD_print( "Keyboard buffer to ascii =\0"); LCD_print_char(a); LCD_set_cursor(0 , 5); LCD_print("`1234567890-=BS \0"); LCD_set_cursor(0 , 6); for(x=1; x<15; x++) { if(ps2_keyboard_state[x] == 1) { LCD_print_char('^'); }else{ LCD_print_char(' '); } } LCD_set_cursor(0 , 7); LCD_print("qwertyuiop[] \0"); LCD_set_cursor(0 , 8); for(x=15; x<30; x++) { if(ps2_keyboard_state[x] == 1) { LCD_print_char('^'); }else{ LCD_print_char(' '); } } LCD_set_cursor(0 , 9); LCD_print("asdfghjkl;'ENT\0"); LCD_set_cursor(0 , 10); for(x=30; x<45; x++) { if(ps2_keyboard_state[x] == 1) { LCD_print_char('^'); }else{ LCD_print_char(' '); } } LCD_set_cursor(0 , 11); LCD_print(" zxcvbnm,./ \0"); LCD_set_cursor(0 , 12); for(x=44; x<59; x++) { if(ps2_keyboard_state[x] == 1) { LCD_print_char('^'); }else{ LCD_print_char(' '); } } data2[9]= a; LCD_set_cursor(0 , 13);LCD_print( data2 ); for(x = 0; x < 9; x++) { data2[x] = data2[x+1]; }
alt = a;} }
z80_outp( Z80_PIO_B, 0x3f);
return 0;}
char kbd_char_bf(void){int x;char a, b;__asmdi__endasm;
a = kbd_buffer[0];b = a;x = 0;
if( kbd_buffer[0] == 0) goto kbd_buff_exit; // Nothing in buffer to print.
if (a == 0xf0){ kbd_up = 1; // Next data is which key released. goto kbd_buff_exit;}
if (a == 0xe0){ goto kbd_buff_exit;}
// Controll keys
// Shift active?
if ( b == 0x12 ){ if (kbd_up == 1) { shift_l = 0; }else{ shift_l = 1; }}
if ( b == 0x59 ){ if (kbd_up == 1) { shift_r = 0; }else{ shift_r = 1; }}
shift_active = shift_l || shift_r;
while( (a != ps2_table[x]) && (x < 76)) x++;
if (x <= 76) {
if (shift_active == 0) { b = ps2_ascii_lower[x]; }else{ b = ps2_ascii_upper[x]; } if( ( kbd_up == 1 ) && (ps2_keyboard_state[x] == 1)) { ps2_keyboard_state[x] = 0; kbd_up = 0; b = 0; goto kbd_buff_exit; }else{ ps2_keyboard_state[x] = 1; } }else{ b = 0;}
if (isascii(b) != 1) b = '*';
kbd_buff_exit:
for(x = 0; x < kbd_ptr; x++) { kbd_buffer[x] = kbd_buffer[x+1]; }if (kbd_ptr == 0) kbd_buffer[0] = 0; if (kbd_ptr != 0) kbd_ptr-- ;
__asmei__endasm; return b; }
void z80_rst_38h(void) __naked{ __asm
push ix push hl di ld hl,0x0001 ld (_int_38),hl //ld hl,_int_38 + 1 pop hl pop ix ei reti
__endasm;}
void isr_pio_0_a(void) __naked{__asm ld hl, 0x0001 ;(ix + 1) ld (_pio_int_a),hl ei reti__endasm; }
void isr_pio_0_b(void) __naked{ __asm di ; reset keyboard to restart send of last data sent ; Z80 PIO port B is set to bit 6 and 7 inputs and 4 and 5 out. ; Bit 5 turns on Transistor pulling Clock line low. push ix push hl push af push bc push de ld a, 0x1f ; out (0x01), a ; bring Clock line low ld hl,0x0064 call _delay ; Delay 100 ms to initiate resend ld a, 0x3f ; release keyboard bring Clock line high out (0x01), a ld a, 0x01 ;debug line turn on LED on port A out (0x00), a ld bc, 0x0000 ; initialize keyboard data ld e, 0x00 ; initialize clock count start_byte: ; Not to confuse by name, but we return here for each bit. ld a, e ; cp 0x0b ; have we processed 11 bits. jp Z, exit_kbdcheck_input: in a, (0x01) bit 7, a jp NZ, check_input ; looking for clock low. bit 6, a ; data one or zero check jp Z, bit_zero set 3, b srl b rr c jp bit_endbit_zero: res 3, b srl b rr cbit_end: inc e ; increase bit countcheck_input_1: ;here wait for clock state to change. in a, (0x01) bit 7, a jp Z, check_input_1 jp start_byteexit_kbd: ;process byte ld (_kbd_tmp), bc ; RAW input data from keyboard srl b ; remove start bit and create a 8 bit keyboard data. rr c ld a, c ld (_kbd), a ld hl, _kbd_ptr ; this is for our keyboard buffer if program ; has not read the keyboard data ld e, (hl) ; Where are we in buffer. ld a, e cp 0x0f ; have we reached end check jp Z, buffer_full ld d, 0x00 ld hl, _kbd_buffer add hl, de ld a, c ld (hl), a ld hl, _kbd_ptr inc e ld (hl), ebuffer_full: ld a, 0x00 ; Turn off Debug LED out (0x00), a pop de pop bc pop af pop hl pop ix ei reti
__endasm; /* __asm ld hl, 0x0001 ;(ix + 1) ld (_pio_int_b),hl ei reti__endasm;*/
}
void Button_press(void){
char button_state = 1;while( button_state == 1 ){if ((z80_inp( Z80_PIO_B) & 0b00001000) == 0) { button_state = 0; } else { button_state = 1; }}
}
void system_init(void){
// initialize PIO ports
z80_outp( Z80_PIO_A_CTL, Z80_PIO_M0); // set mode 0 byte outz80_outp( Z80_PIO_B_CTL, Z80_PIO_M3); // set mode 3 bit in/out mode mask selectz80_outp( Z80_PIO_B_CTL, 0xcf); // bit's 0-3 and 6&7 inputs, 4&5 outputs.
// intialize displayLCD_write_cmd( 0x40 ); // System set commandLCD_write(0x30); // P1 use internal 8px char w/ no top line correctionLCD_write(0x87); // P2 8px width charLCD_write(0x07); // P3 8px height charLCD_write(0x1f); // P4 32 char per lineLCD_write(0x23); // P5 previous value + 4LCD_write(0x7f); // P6 128 pixel screen heightLCD_write(0x20); // P7 32 char per lineLCD_write(0x00); // P8
LCD_write_cmd(0x5d); // Set cursor typeLCD_write(0x04);LCD_write(0x86);LCD_write_cmd(0x4c); // Set direction of cursor movementLCD_write_cmd(0x5B); // Set display overlayLCD_write(0x08); //3
LCD_write_cmd(0x44); //Scroll - Set display start address and display regionsLCD_write(0x00);LCD_write(0x00);LCD_write(0x80);LCD_write(0xb0);LCD_write(0x04);LCD_write(0x80);LCD_write(0x00);LCD_write(0x00);LCD_write(0x80);LCD_write(0xb0);
LCD_write_cmd(0x5A); // Set horizontal scroll LCD_write(0x00);
LCD_write_cmd(0x59); // Display onLCD_write(0x16); // 06
LCD_clear();LCD_graphics_clear();LCD_set_cursor(0, 0);
}
void int2ascii(unsigned int cx, char *ptr ){ int i;ptr = ptr + 5;
*ptr-- = '\0';
for( i = 0; i < 5; i++){*ptr-- = '0' + cx % 10 ;cx = cx / 10;} }
#include "Hyundai_256x128.h"#include "Z80_IO.h"#include "ps2_keyboard.h"#include <z80.h>#include <stdlib.h>#include <ctype.h>
extern void isr_pio_0_a(void);extern void isr_pio_0_b(void);extern int vid_pio_0_a;extern int vid_pio_0_b;
void int2ascii(unsigned int cx, char *ptr );void system_init(void);void Button_press(void);char kbd_char_bf(void);
int pio_int_a = 0, pio_int_b = 0, int_38 = 0, add_isr = 0 , kbd_tmp = 0;char kbd_bit=0;
char kbd_buffer[16], kbd_char, kbd_up = 0, kbd_clt = 0, kbd_last_char = 0, kbd_ptr = 0 , kbd = 0;
char shift_r = 0, shift_l = 0, shift_active = 0;
void delay(int j){int i;for(i=0; i<j; i++);}
int main(){
char a, data[10], data2[11]; int x, int_38_count = 0, port_a = 0, port_b = 0, couter_1 = 0, pio_a_couter = 0, pio_b_couter = 0, alt, k[4] ;
data2[10] = 0;
system_init();
LCD_set_cursor(0 , 0);LCD_print("Interrupt test\0");z80_outp( Z80_PIO_A_CTL, Z80_PIO_DI);z80_outp( Z80_PIO_B_CTL, Z80_PIO_DI);
/*__asm ld hl, _vid_pio_0_a ld (_add_isr),hl im 1 ei
__endasm;
*///z80_outp( Z80_PIO_A_CTL, Z80_PIO_EI);
// set up Z80 PIO vector interrupts
__asm di ld hl, _vid_pio_0_a ld a, l out (0x02), a ld hl, _vid_pio_0_b ld a, l out (0x03), a //ld a, h //ld i, a im 2 ei__endasm;
for(x=0;x<76;x++){ps2_keyboard_state[x] = 0;}
LCD_clear();LCD_set_cursor(0 , 0);LCD_print("PS/2 Keyboard test\0");kbd_tmp = 0;pio_int_b = 0;kbd_bit = 0;alt = 0;port_b = z80_inp( Z80_PIO_B ); //Z80 PIO port B;z80_outp( Z80_PIO_B, 0x1f);__asm di__endasm;z80_outp( Z80_PIO_B_CTL, Z80_PIO_EI | Z80_PIO_EI_MF | Z80_PIO_EI_LOW |Z80_PIO_EI_AND ); // interrupt with mask 0x97z80_outp( Z80_PIO_B_CTL, 0x7f); // monitor port bit 2 0x3f__asm ei__endasm;
delay(100);
z80_outp( Z80_PIO_B, 0x3f);
while( port_b != 0xcc){
a = kbd_char_bf();
if( a != 0 ){ LCD_set_cursor(0 , 1); LCD_print( "Keyboard =\0"); int2ascii( kbd_last_char, data); LCD_print( data ); int2ascii( kbd, data); LCD_print( data ); LCD_set_cursor(0 , 2); LCD_print( "Keyboard buffer =\0"); int2ascii( kbd_ptr, data); LCD_print( data );kbd_last_char = kbd; LCD_set_cursor(0 , 3); LCD_print( "Keyboard buffer to ascii =\0"); LCD_print_char(a); LCD_set_cursor(0 , 5); LCD_print("`1234567890-=BS \0"); LCD_set_cursor(0 , 6); for(x=1; x<15; x++) { if(ps2_keyboard_state[x] == 1) { LCD_print_char('^'); }else{ LCD_print_char(' '); } } LCD_set_cursor(0 , 7); LCD_print("qwertyuiop[] \0"); LCD_set_cursor(0 , 8); for(x=15; x<30; x++) { if(ps2_keyboard_state[x] == 1) { LCD_print_char('^'); }else{ LCD_print_char(' '); } } LCD_set_cursor(0 , 9); LCD_print("asdfghjkl;'ENT\0"); LCD_set_cursor(0 , 10); for(x=30; x<45; x++) { if(ps2_keyboard_state[x] == 1) { LCD_print_char('^'); }else{ LCD_print_char(' '); } } LCD_set_cursor(0 , 11); LCD_print(" zxcvbnm,./ \0"); LCD_set_cursor(0 , 12); for(x=44; x<59; x++) { if(ps2_keyboard_state[x] == 1) { LCD_print_char('^'); }else{ LCD_print_char(' '); } } data2[9]= a; LCD_set_cursor(0 , 13);LCD_print( data2 ); for(x = 0; x < 9; x++) { data2[x] = data2[x+1]; }
alt = a;} }
z80_outp( Z80_PIO_B, 0x3f);
return 0;}
char kbd_char_bf(void){int x;char a, b;__asmdi__endasm;
a = kbd_buffer[0];b = a;x = 0;
if( kbd_buffer[0] == 0) goto kbd_buff_exit; // Nothing in buffer to print.
if (a == 0xf0){ kbd_up = 1; // Next data is which key released. goto kbd_buff_exit;}
if (a == 0xe0){ goto kbd_buff_exit;}
// Controll keys
// Shift active?
if ( b == 0x12 ){ if (kbd_up == 1) { shift_l = 0; }else{ shift_l = 1; }}
if ( b == 0x59 ){ if (kbd_up == 1) { shift_r = 0; }else{ shift_r = 1; }}
shift_active = shift_l || shift_r;
while( (a != ps2_table[x]) && (x < 76)) x++;
if (x <= 76) {
if (shift_active == 0) { b = ps2_ascii_lower[x]; }else{ b = ps2_ascii_upper[x]; } if( ( kbd_up == 1 ) && (ps2_keyboard_state[x] == 1)) { ps2_keyboard_state[x] = 0; kbd_up = 0; b = 0; goto kbd_buff_exit; }else{ ps2_keyboard_state[x] = 1; } }else{ b = 0;}
if (isascii(b) != 1) b = '*';
kbd_buff_exit:
for(x = 0; x < kbd_ptr; x++) { kbd_buffer[x] = kbd_buffer[x+1]; }if (kbd_ptr == 0) kbd_buffer[0] = 0; if (kbd_ptr != 0) kbd_ptr-- ;
__asmei__endasm; return b; }
void z80_rst_38h(void) __naked{ __asm
push ix push hl di ld hl,0x0001 ld (_int_38),hl //ld hl,_int_38 + 1 pop hl pop ix ei reti
__endasm;}
void isr_pio_0_a(void) __naked{__asm ld hl, 0x0001 ;(ix + 1) ld (_pio_int_a),hl ei reti__endasm; }
void isr_pio_0_b(void) __naked{ __asm di ; reset keyboard to restart send of last data sent ; Z80 PIO port B is set to bit 6 and 7 inputs and 4 and 5 out. ; Bit 5 turns on Transistor pulling Clock line low. push ix push hl push af push bc push de ld a, 0x1f ; out (0x01), a ; bring Clock line low ld hl,0x0064 call _delay ; Delay 100 ms to initiate resend ld a, 0x3f ; release keyboard bring Clock line high out (0x01), a ld a, 0x01 ;debug line turn on LED on port A out (0x00), a ld bc, 0x0000 ; initialize keyboard data ld e, 0x00 ; initialize clock count start_byte: ; Not to confuse by name, but we return here for each bit. ld a, e ; cp 0x0b ; have we processed 11 bits. jp Z, exit_kbdcheck_input: in a, (0x01) bit 7, a jp NZ, check_input ; looking for clock low. bit 6, a ; data one or zero check jp Z, bit_zero set 3, b srl b rr c jp bit_endbit_zero: res 3, b srl b rr cbit_end: inc e ; increase bit countcheck_input_1: ;here wait for clock state to change. in a, (0x01) bit 7, a jp Z, check_input_1 jp start_byteexit_kbd: ;process byte ld (_kbd_tmp), bc ; RAW input data from keyboard srl b ; remove start bit and create a 8 bit keyboard data. rr c ld a, c ld (_kbd), a ld hl, _kbd_ptr ; this is for our keyboard buffer if program ; has not read the keyboard data ld e, (hl) ; Where are we in buffer. ld a, e cp 0x0f ; have we reached end check jp Z, buffer_full ld d, 0x00 ld hl, _kbd_buffer add hl, de ld a, c ld (hl), a ld hl, _kbd_ptr inc e ld (hl), ebuffer_full: ld a, 0x00 ; Turn off Debug LED out (0x00), a pop de pop bc pop af pop hl pop ix ei reti
__endasm; /* __asm ld hl, 0x0001 ;(ix + 1) ld (_pio_int_b),hl ei reti__endasm;*/
}
void Button_press(void){
char button_state = 1;while( button_state == 1 ){if ((z80_inp( Z80_PIO_B) & 0b00001000) == 0) { button_state = 0; } else { button_state = 1; }}
}
void system_init(void){
// initialize PIO ports
z80_outp( Z80_PIO_A_CTL, Z80_PIO_M0); // set mode 0 byte outz80_outp( Z80_PIO_B_CTL, Z80_PIO_M3); // set mode 3 bit in/out mode mask selectz80_outp( Z80_PIO_B_CTL, 0xcf); // bit's 0-3 and 6&7 inputs, 4&5 outputs.
// intialize displayLCD_write_cmd( 0x40 ); // System set commandLCD_write(0x30); // P1 use internal 8px char w/ no top line correctionLCD_write(0x87); // P2 8px width charLCD_write(0x07); // P3 8px height charLCD_write(0x1f); // P4 32 char per lineLCD_write(0x23); // P5 previous value + 4LCD_write(0x7f); // P6 128 pixel screen heightLCD_write(0x20); // P7 32 char per lineLCD_write(0x00); // P8
LCD_write_cmd(0x5d); // Set cursor typeLCD_write(0x04);LCD_write(0x86);LCD_write_cmd(0x4c); // Set direction of cursor movementLCD_write_cmd(0x5B); // Set display overlayLCD_write(0x08); //3
LCD_write_cmd(0x44); //Scroll - Set display start address and display regionsLCD_write(0x00);LCD_write(0x00);LCD_write(0x80);LCD_write(0xb0);LCD_write(0x04);LCD_write(0x80);LCD_write(0x00);LCD_write(0x00);LCD_write(0x80);LCD_write(0xb0);
LCD_write_cmd(0x5A); // Set horizontal scroll LCD_write(0x00);
LCD_write_cmd(0x59); // Display onLCD_write(0x16); // 06
LCD_clear();LCD_graphics_clear();LCD_set_cursor(0, 0);
}
void int2ascii(unsigned int cx, char *ptr ){ int i;ptr = ptr + 5;
*ptr-- = '\0';
for( i = 0; i < 5; i++){*ptr-- = '0' + cx % 10 ;cx = cx / 10;} }
The assembly routine from above, waits to read each bit before exiting
void isr_pio_0_b(void) __naked{ __asm di ; reset keyboard to restart send of last data sent ; Z80 PIO port B is set to bit 6 and 7 inputs and 4 and 5 out. ; Bit 5 turns on Transistor pulling Clock line low. push ix push hl push af push bc push de ld a, 0x1f ; out (0x01), a ; bring Clock line low ld hl,0x0064 call _delay ; Delay 100 ms to initiate resend ld a, 0x3f ; release keyboard bring Clock line high out (0x01), a ld a, 0x01 ;debug line turn on LED on port A out (0x00), a ld bc, 0x0000 ; initialize keyboard data ld e, 0x00 ; initialize clock count start_byte: ; Not to confuse by name, but we return here for each bit. ld a, e ; cp 0x0b ; have we processed 11 bits. jp Z, exit_kbdcheck_input: in a, (0x01) bit 7, a jp NZ, check_input ; looking for clock low. bit 6, a ; data one or zero check jp Z, bit_zero set 3, b srl b rr c jp bit_endbit_zero: res 3, b srl b rr cbit_end: inc e ; increase bit countcheck_input_1: ;here wait for clock state to change. in a, (0x01) bit 7, a jp Z, check_input_1 jp start_byteexit_kbd: ;process byte ld (_kbd_tmp), bc ; RAW input data from keyboard srl b ; remove start bit and create a 8 bit keyboard data. rr c ld a, c ld (_kbd), a ld hl, _kbd_ptr ; this is for our keyboard buffer if program ; has not read the keyboard data ld e, (hl) ; Where are we in buffer. ld a, e cp 0x0f ; have we reached end check jp Z, buffer_full ld d, 0x00 ld hl, _kbd_buffer add hl, de ld a, c ld (hl), a ld hl, _kbd_ptr inc e ld (hl), ebuffer_full: ld a, 0x00 ; Turn off Debug LED out (0x00), a pop de pop bc pop af pop hl pop ix ei reti
__endasm;
void isr_pio_0_b(void) __naked{ __asm di ; reset keyboard to restart send of last data sent ; Z80 PIO port B is set to bit 6 and 7 inputs and 4 and 5 out. ; Bit 5 turns on Transistor pulling Clock line low. push ix push hl push af push bc push de ld a, 0x1f ; out (0x01), a ; bring Clock line low ld hl,0x0064 call _delay ; Delay 100 ms to initiate resend ld a, 0x3f ; release keyboard bring Clock line high out (0x01), a ld a, 0x01 ;debug line turn on LED on port A out (0x00), a ld bc, 0x0000 ; initialize keyboard data ld e, 0x00 ; initialize clock count start_byte: ; Not to confuse by name, but we return here for each bit. ld a, e ; cp 0x0b ; have we processed 11 bits. jp Z, exit_kbdcheck_input: in a, (0x01) bit 7, a jp NZ, check_input ; looking for clock low. bit 6, a ; data one or zero check jp Z, bit_zero set 3, b srl b rr c jp bit_endbit_zero: res 3, b srl b rr cbit_end: inc e ; increase bit countcheck_input_1: ;here wait for clock state to change. in a, (0x01) bit 7, a jp Z, check_input_1 jp start_byteexit_kbd: ;process byte ld (_kbd_tmp), bc ; RAW input data from keyboard srl b ; remove start bit and create a 8 bit keyboard data. rr c ld a, c ld (_kbd), a ld hl, _kbd_ptr ; this is for our keyboard buffer if program ; has not read the keyboard data ld e, (hl) ; Where are we in buffer. ld a, e cp 0x0f ; have we reached end check jp Z, buffer_full ld d, 0x00 ld hl, _kbd_buffer add hl, de ld a, c ld (hl), a ld hl, _kbd_ptr inc e ld (hl), ebuffer_full: ld a, 0x00 ; Turn off Debug LED out (0x00), a pop de pop bc pop af pop hl pop ix ei reti
__endasm;