INS 8154 PIO+SRAM ================= 7 6 5 4 3 2 1 0 --------------- 0 0 0 d p n n n | | +-+-+--bit number | +--------port A/B +----------set bit/read bit 0 0 1 x x m d p | | +--port A/B | +----data register/data direction register +------port/mode register 0 1 x x x x x x 1 x x x x x x x Read/Write SRAM data byte Write Read 00+n Clear bit n of Port A Read bit n of Port A 08+n Clear bit n of Port B Read bit n of Port B 10+n Set bit n of Port A Read bit n of Port A 18+n Set bit n of Port A Read bit n of Port B 20 Write to Port A Read from Port A 21 Write to Port B Read from Port B 22 Write ODP Port A 23 Write ODP Port B 24 Write Mode Register 80+n read/write SRAM