penguin86/pato-z80-home-computer
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Fixed timings

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This commit is contained in:
Daniele Verducci su MatissePenguin 2021-01-03 15:30:06 +01:00
parent c0f7049df9
commit 09785e1317
1 changed files with 12 additions and 6 deletions
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18
pat80-io-devices/composite-pal-adapter/software/avr-assembly/main.asm
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@ -6,6 +6,7 @@
; define constant
.equ SYNC_PIN = PD7 ; Sync pin is on Port D 7 (pin 21)
.equ VIDEO_PIN = PD6 ; Video pin is on Port D 6 (pin 20)
.equ DEBUG_PIN = PD5 ; Video pin is on Port D 5 (pin 19)
; start vector
.org 0x0000
@ -15,6 +16,7 @@
main:
sbi DDRD, SYNC_PIN ; set pin as output
sbi DDRD, VIDEO_PIN ; set pin as output
sbi DDRD, DEBUG_PIN ; set pin as output
v_refresh_loop:
; start 5 long sync pulses
@ -49,8 +51,6 @@ v_refresh_loop:
cbi PORTD, VIDEO_PIN ; video goes low ; 2 cycle
brne l_sync_video_loop1 ; 2 cycle if true, 1 if false
cbi PORTD, VIDEO_PIN ; video goes low
ldi r18, 137 ; 1 cycle
l_sync_video_loop2:
dec r18 ; 1 cycle
@ -79,8 +79,14 @@ v_refresh_loop:
call short_sync
call short_sync
call short_sync
call short_sync
; end 6 short sync pulses
; debug
sbi PORTD, DEBUG_PIN ; high
cbi PORTD, DEBUG_PIN ; low
; debug
jmp v_refresh_loop
; end vertical refresh
@ -98,7 +104,7 @@ long_sync:
sbi PORTD, SYNC_PIN ; sync goes high (0.3v)
ldi r18, 16 ; 1 cycle
ldi r18, 15 ; 1 cycle
long_sync_high_loop: ; requires 3 cpu cycles
dec r18 ; 1 cycle
brne long_sync_high_loop ; 2 cycle if true, 1 if false
@ -106,13 +112,13 @@ long_sync:
ret
short_sync:
; short sync: 2uS low (48 cycles @ 24Mhz), 30uS high
; short sync: 2uS low (48 cycles @ 24Mhz), 30uS high (720 cycles @ 24Mhz)
cbi PORTD, SYNC_PIN ; sync goes low (0v) ; 2 cycle
ldi r18, 16 ; 1 cycle
ldi r18, 15 ; 1 cycle
short_sync_low_loop: ; requires 3 cpu cycles
dec r18 ; 1 cycle
brne long_sync_low_loop ; 2 cycle if true, 1 if false
brne short_sync_low_loop ; 2 cycle if true, 1 if false
sbi PORTD, SYNC_PIN ; sync goes high (0.3v)