Atic Atac: Routine at 39873

39873: Screen Address One Pixel Below

Moves a screen buffer address down by one pixel line.

Input
HL	The screen buffer address

Output
HL	The screen buffer address of the line below

ScreenPosition1PixelBelow

39873

INC H

Move down a pixel line.

39874

LD A,H

Fetch the high byte of the address.

39875

AND %00000111

Keep only bits 0-2.

39877

RET NZ

Return if a character boundary has not been crossed.

39878

LD A,L

Fetch the low byte of the address.

39879

ADD A,32

Move down a character row.

39881

LD L,A

Keep the new low byte in L.

39882

AND %11100000

Keep only bits 5-7.

39884

RET Z

Return if the next third of the screen has been reached.

39885

LD A,H

Fetch the high byte of the address.

39886

SUB 8

Subtract 8.

39888

LD H,A

Keep the new high byte in H.

39889

RET

Return.

View the equivalent code in;