xor ah,ah                    ; clear ah, since i will be using AX
mov al,[si+8]                ; pixel 8 from 256 color source
shl ax,5                     ; ax = pIN[X] shl 5
add bp,ax                    ; +PY (dither row position)
mov dx,[bp+ColorPat]         ; pixels pattern for line 1/2 (dither column 0-1, row 0-1)
sub bp, ax                   ; keep BP with just dither row position (PY)
mov [es:di+2], dl            ; - 8 bit (first unroll the write)
; instruction
; instruction (+/- 3 instruction latency time between video writes...)
; instruction
mov [es:di+82], dh           ; - 8 bit (first unroll the write)