This subroutine is called by POINT_SUB and by PLOT. Is is entered with the co-ordinates of a pixel in the BC register pair and returns with HL holding the address of the display file byte which contains that pixel and A pointing to the position of the pixel within the byte.
Input
Output
PIXEL_ADD
08874
LD A,175
Test that the y co-ordinate (in B) is not greater than 175.