Apple Macintosh XL Serial B 25 pin

25 pin D-SUB male connector.

25 pin D-SUB female connector.

The Serial B port on the Apple Lisa and its successor the Macintosh XL (Lisa 2 rebranded) is a DB-25 male connector supporting RS-232-C compatible asynchronous serial communication at speeds from 300 to 57,600 bps. Unlike Serial A, it carries no synchronous clock lines, making it suitable primarily for modem connections and LocalTalk/AppleTalk networking. Pin 19 carries AppleTalk receive data, enabling the port’s use in LocalTalk networks via an appropriate adapter. The connector is found on all Lisa and Macintosh XL units produced by Apple between 1983 and 1985.

Signals

• TxD- — Transmit Data (serial data output from the computer to the peripheral)
• RxD- — Receive Data (serial data input to the computer from the peripheral)
• HSK/DSR — Handshake / Data Set Ready; connected to the SCC’s TRxCB or CTSB input, used for flow control
• RxD+ — AppleTalk Receive Data; carries LocalTalk receive data when the port is used in a LocalTalk network
• TxD+/DTR — Connected to DTRB (Data Terminal Ready B); in LocalTalk operation this line also serves the transmit data positive leg

Notes

• The connector on the computer is DB-25 male; the mating cable connector is DB-25 female.
• Only six pins are active; all remaining pins are not connected.
• Pin 19 carried AppleTalk receive data for LocalTalk operation, distinguishing Serial B from the more fully featured Serial A port.
• The port supports RS-232-C single-ended signalling; it does not implement the RS-422 differential pairs present on later Macintosh serial ports (mini-DIN-8).
• Data rates of 300 to 57,600 bps are supported in asynchronous mode.

References

• Apple Technical Procedures Peripheral Interface Guide (PN 072-0213D) — Apple Computer, Inc., March 1989

Category:Serial Connectors