video_int.h
//-----------video---------------- //cycles = 63.625 * 16 Note NTSC is 63.55 //but this line duration makes each frame exactly 1/60 sec //which is nice for keeping a realtime clock #define lineTime 1018 #define width 126 #define ScreenTop 30 #define ScreenBot 230 extern char syncON, syncOFF; int LineCount; #pragma warn- interrupt [TIM1_COMPA] void t1_cmpA(void) { //start the Horizontal sync pulse PORTD = syncON; //update the curent scanline number LineCount ++ ; //begin inverted (Vertical) synch after line 247 if (LineCount==248) { syncON = 0b00100000; syncOFF = 0; } //back to regular sync after line 250 if (LineCount==251) { syncON = 0; syncOFF = 0b00100000; } //start new frame after line 262 if (LineCount==263) { LineCount = 1; } delay_us(2); PORTD = syncOFF; if (LineCount=ScreenTop) { //compute byte index for beginning of the next line //left-shift 4 would be individual lines // <<3 means line-double the pixels //The 0xfff8 truncates the odd line bit //i=(LineCount-ScreenTop)<<3 & 0xfff8; // #asm push r16 lds r12, _LineCount lds r13, _Linecount+1 ldi r16, 30 sub r12, r16 ldi r16,0 sbc r13, r16 lsl r12 rol r13 lsl r12 rol r13 lsl r12 rol r13 mov r16,r12 andi r16,0xf0 mov r12,r16 pop r16 #endasm //load 16 registers with screen info #asm push r14 push r15 push r16 push r17 push r18 push r19 push r26 push r27 ldi r26,low(_screen) ;base address of screen ldi r27,high(_screen) add r26,r12 ;offset into screen (add i) adc r27,r13 ld r4,x+ ;load 16 registers and inc pointer ld r5,x+ ld r6,x+ ld r7,x+ ld r8,x+ ld r9,x+ ld r10,x+ ld r11,x+ ld r12,x+ ld r13,x+ ld r14,x+ ld r15,x+ ld r16,x+ ld r17,x+ ld r18,x+ ld r19,x pop r27 pop r26 #endasm delay_us(4); //adjust to center image on screen to work with 64 cycles // delay_us(1); //16cycles plus 4 above was added to recenter the image //might have to adjust //blast 16 bytes to the screen #asm ;but first a macro to make the code shorter ;the macro takes a register number as a parameter ;and dumps its bits serially to portD.6 ;the nop can be eliminated to make the display narrower .macro videobits ;regnum BST @0,7 IN R30,0x12 BLD R30,6 nop OUT 0x12,R30 BST @0,6 IN R30,0x12 BLD R30,6 nop OUT 0x12,R30 BST @0,5 IN R30,0x12 BLD R30,6 nop OUT 0x12,R30 BST @0,4 IN R30,0x12 BLD R30,6 nop OUT 0x12,R30 BST @0,3 IN R30,0x12 BLD R30,6 nop OUT 0x12,R30 BST @0,2 IN R30,0x12 BLD R30,6 nop OUT 0x12,R30 BST @0,1 IN R30,0x12 BLD R30,6 nop OUT 0x12,R30 BST @0,0 IN R30,0x12 BLD R30,6 nop OUT 0x12,R30 .endm videobits r4 ;video line -- byte 1 videobits r5 ;byte 2 videobits r6 ;byte 3 videobits r7 ;byte 4 videobits r8 ;byte 5 videobits r9 ;byte 6 videobits r10 ;byte 7 videobits r11 ;byte 8 videobits r12 ;byte 9 videobits r13 ;byte 10 videobits r14 ;byte 11 videobits r15 ;byte 12 videobits r16 ;byte 13 videobits r17 ;byte 14 videobits r18 ;byte 15 videobits r19 ;byte 16 clt ;clear video after the last pixel on the line IN R30,0x12 BLD R30,6 OUT 0x12,R30 pop r19 pop r18 pop r17 pop r16 pop r15 pop r14 #endasm } } #pragma warn+