Write vert and horiz position of beam, or lightpen Bit 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00 V7 V6 V5 V4 V3 V2 V1 V0 H8 H7 H6 H5 H4 H3 H2 H1 Resolution = 1/160 of screen width (280 ns).