6551 Asynchronous serial interface controller (Rockwell). +--------------+ GND |1 +--+ 28| R//W CS0 |2 27| CLK /CS1 |3 26| /IRQ /RST |4 25| D7 RxC |5 24| D6 X1 |6 23| D5 X0 |7 6551 22| D4 /RTS |8 21| D3 /CTS |9 20| D2 TxD |10 19| D1 /DTR |11 18| D0 RxD |12 17| /DSR RS0 |13 16| /DCD RS1 |14 15| VCC +--------------+ [This information is part of the GIICM]