define StringRam $1200                    ;not actually used in the code, but it's here for clarity.
define z_BC $00                           ;fake Z80-style register for pseudo-16-bit operations.
define z_C $00                            ;6502 uses the low byte as the reference point for indirect lookups.
define z_B $01                            ;high byte
define tempMath $02                       ;temp storage of input
define tempBitMask $03                    ;temp storage of the bit filter

lda #$12
sta z_B
lda #$00
sta z_C                                   ;load address $1200 into zero page memory for an indirect lookup.

lda #$0F                                  ;test value
LDY #0                                    ;initialize offset to zero

jsr Hex2BinAscii
brk                                       ;on easy6502 this terminates the program.

Hex2BinAscii:
sta tempMath                              ;store our input, in this case #$0F
lda #%10000000
sta tempBitMask

loop_Hex2BinAscii:
lda tempMath                              ;load input into accumulator.
and tempBitMask                           ;filter out all bits except the one we are checking this pass of the loop
bne bitIsOne
	lda #$30                          ;ascii for zero
	bne StoreBit
bitIsOne:
	lda #$31                          ;ascii for one
StoreBit:
	sta (z_BC),y                      ;store in StringRam+Y
loopOverhead:
	iny                               ;y++
	lsr tempBitMask                   ;shift to next bit in sequence
	beq loop_Hex2BinAscii             ;if mask is zero, we are done. BCC would have worked here as well.
lda #$00                                  ;load the null terminator
sta (z_BC),y	                          ;store the null terminator after the string
rts