Signetics 2650 & 2636 programming/Tutorial code - sync to VRST

Tutorial code - Sync to VRST

This is the code for the tutorial Sync to VRST

; Tutorial SyncVRST
;=============================================================================
        org     0
reset_vector:                   ; the microprocessor starts here when the reset button is pressed
        bcta,un reset
        org     3
interrupt_vector:               ; interrupts shouldn't happen, but we set this just in case
        retc,un
reset:  
        lodi,r0 $20	        ; initialise program status word, just to be sure!
        lpsu                    ; inhibit interrupts, stack pointer=0
        lpsl                    ; register bank 0, without carry, arithmetic compare

        eorz    r0
        stra,r0 effects         ;initialise the 74LS378
        stra,r0 objectsize      ;all objects size 0
        bsta,un DefineObjects   ;define all objects 
   
        lodi,r0 $AA
        stra,r0 score12
        stra,r0 score34

        eorz    r0
        stra,r0 effects         ; !invert = 0 

        lodi,r0 0               ;  X / 000              /   0     / 000
        stra,r0 backgnd         ;    / black background / disabled / yellow screen

        lodi,r0 %00011101       ; XX  /  011        /   101
        stra,r0 colours12       ;     / obj1 red / obj2 green
        lodi,r0 %00110000       ; XX  /  110        /   000
        stra,r0 colours34       ;     / obj 3 blue / 4 white
endless:
        bsta,un Vsync0          ; make sure VRST hasn't started
        bsta,un Vsync1          ; wait for VRST to start

        loda,r0 vc1		; increment vertical position of object 1
        addi,r0 1
        stra,r0 vc1

        loda,r0 hc1		; decrement horizontal position of object 1
        subi,r0 1
        stra,r0 hc1

        bctr,un endless

;===================================================================
; subroutine  -  define shapes and position of all objects
                       
DefineObjects:
        lodi,r3 $0E
        lodi,r0 $FF
loopDS:                         
        stra,r0 shape1,r3-      ; create rectangular shapes
        stra,r0 shape2,r3
        stra,r0 shape3,r3
        stra,r0 shape4,r3
        brnr,r3 loopDS

        retc,un

;=================================================================
; subroutine - wait for VRST to clear
Vsync0:                       
        tpsu    sense
        bctr,eq Vsync0          ; wait for Sense bit to clear
        retc,un
;=================================================================
; subroutine - wait for VRST to set
Vsync1:         
        tpsu    sense           ; wait for Sense bit to be set
        bctr,lt Vsync1
        retc,un
;=================================================================