* * File: cylon_c.asm * Program to control LEDs on PORT C, flashing * them back and forth. * Tom Dickens 8/21/1998 * * Assumes an 'E1 or 'A1 device. * Change \$B600 to \$F800 for 'E2 ORG \$B600 * * Initialize PORT C for output * ldaa #\$FF staa \$1007 ; data direction for Port C (0=in, 1=out) * Top: ldx #TABLE ; X points to the data in the TABLE Loop: ldaa 0,X ; load the data from the TABLE beq Top ; if we read the zero, start over staa \$1003 ; store value from TABLE to Port C bsr Delay ; wait a while inx ; x = x + 1, point to next value in TABLE bra Loop ; do it again... * * Subroutine to delay half a second / 14 = 035.7 mS * 1 cycle = 500 nS. Each X loop takes 6 cycles, or 3uS. * Each Y loop takes 10 + 6 X cycles, for an equation of: * delay_time = 14 * (24 + Y (10 + 6 X) ) 500 nS * Now we need to solve for X and Y to get 0.5 S. * X=3330 and Y=50 gives us 0.4999912 S. * Delay: pshx ; remember X (4 cycles) pshy ; remember Y (5 cycles) ldy #4 ; (4 cycles) LoopY: ldx #2973 ; (3 cycles) LoopX: dex ; x = x - 1 (3 cycles) bne LoopX ; if x!= 0, loop (3 cycles) * dey ; y = y - 1 (4 cycles) bne LoopY ; if y!= 0, loop (3 cycles) * puly ; restore Y (6 cycles) pulx ; restore X (5 cycles) rts * * The following table is data we will read in for the LED values. * These values exist as data values in the program. The values * end with a zero, which causes the reading program to loop. * TABLE: fcb \$01, \$02, \$04, \$08, \$10, \$20, \$40, \$80 fcb \$40, \$20, \$10, \$08, \$04, \$02, \$00