The Apple Serial NB Card is a NuBus expansion card designed for the Macintosh II family of computers, providing multiple RS-232C serial ports — four RS-232C channels, or alternatively one V.35 plus one RS-232C configuration. It uses a high-density 62-pin connector whose signal assignments span four independent channels (CHA1, CHB1, CHA2, CHB2), each carrying the standard RS-232C modem-control lines (RTS, CTS, DSR, DTR, DCD, RI) alongside RS-422 differential data and clock pairs for the first two channel pairs. The card was intended for applications requiring multiple simultaneous serial connections, such as multi-user gateway or WAN configurations on the Macintosh II platform.
| Pin | Signal | Description | Direction |
|---|---|---|---|
| 1 | +CA1F | X.21 control, +CHA1 | output |
| 2 | 232TXDA1 | Transmit data, CHA1, RS-232 | output |
| 3 | -CA1F | X.21 control, -CHA1 | output |
| 4 | 1RTSA | Ready To Send, CHA1, RS-232 | output |
| 5 | 1CTSA | Clear To Send, CHA1, RS-232 | input |
| 6 | +CB1F | X.21 control, +CHB1 | output |
| 7 | 232TXDB1 | Transmit data, CHB1, RS-232 | output |
| 8 | -CB1F | X.21 control, -CHB1 | output |
| 9 | 1RTSB | Ready To Send, CHB1, RS-232 | output |
| 10 | 1CTSB | Clear To Send, CHB1, RS-232 | input |
| 11 | +1B1 | X.21 indication, +CHB1 | input |
| 12 | 232TXDA2 | Transmit data, CHA2, RS-232 | output |
| 13 | 2RXDA | Receive data, CHA2, RS-232 | input |
| 14 | 2RTSA | Ready To Send, CHA2, RS-232 | output |
| 15 | 2CTSA | Clear To Send, CHA2, RS-232 | input |
| 16 | +IA1 | X.21 indication, +CHA1 | input |
| 17 | 232TXDB2 | Transmit data, CHB2, RS-232 | output |
| 18 | 2RXDB | Receive data, CHB2, RS-232 | input |
| 19 | 2RTSB | Ready To Send, CHB2, RS-232 | output |
| 20 | 2CTSB | Clear To Send, CHB2, RS-232 | input |
| 21 | +422TXCA1 | +Transmit clock, CHA1, RS-422 | input |
| 22 | -422TXCA1 | -Transmit clock, CHA1, RS-422 | input |
| 23 | +422RXDA1 | +Receive data, CHA1, RS-422 | input |
| 24 | -422RXDA1 | -Receive data, CHA1, RS-422 | input |
| 25 | +422RXCA1 | +Receive clock, CHA1, RS-422 | input |
| 26 | -422RXCA1 | -Receive clock, CHA1, RS-422 | input |
| 27 | +422TXDA1 | +Transmit data, CHA1, RS-422 | output |
| 28 | -422TXDA1 | -Transmit data, CHA1, RS-422 | output |
| 29 | +422TXCB1 | +Transmit clock, CHB1, RS-422 | input |
| 30 | -422TXCB1 | -Transmit clock, CHB1, RS-422 | input |
| 31 | +422RXDB1 | +Receive data, CHB1, RS-422 | input |
| 32 | -422RXDB1 | -Receive data, CHB1, RS-422 | input |
| 33 | +422RXCB1 | +Receive clock, CHB1, RS-422 | input |
| 34 | -422RXCB1 | -Receive clock, CHB1, RS-422 | input |
| 35 | +422TXDB1 | +Transmit data, CHB1, RS-422 | output |
| 36 | -422TXDB1 | -Transmit data, CHB1, RS-422 | output |
| 37 | GND_6 | Extra ground | |
| 38 | 2TXCA | Transmit clock, CHA2, RS-232 | input |
| 39 | 2RXCA | Receive clock, CHA2, RS-232 | input |
| 40 | 2RXCB | Receive clock, CHB2, RS-232 | input |
| 41 | GND_5 | Extra ground | |
| 42 | 2TXCB | Transmit clock, CHB2, RS-232 | input |
| 43 | 1DSRA | Data Set Ready, CHA1, RS-232 | input |
| 44 | 1DCDA/-IA1 | Data Carrier Detect, RS-232/X.21 indication, -CHA1 | input |
| 45 | 1DTRA | Data Terminal Ready, CHA1, RS-232 | output |
| 46 | 1RIA | Ring Indicator, CHA1, RS-232 | input |
| 47 | GND_4 | CHB2 ground | |
| 48 | 1DSRB | Data Set Ready, CHB1, RS-232 | input |
| 49 | 1DCDB/-IB1 | Data Carrier Detect, RS-232/X.21 indication, -CHB1 | input |
| 50 | 1DTRB | Data Terminal Ready, CHB1, RS-232 | output |
| 51 | 1RIB | Ring Indicator, CHB1, RS-232 | input |
| 52 | GND_3 | CHA2 ground | |
| 53 | 2DSRA | Data Set Ready, CHA2, RS-232 | input |
| 54 | 2DCDA | Data Carrier Detect, CHA2, RS-232 | input |
| 55 | 2DTRA | Data Terminal Ready, CHA2, RS-232 | output |
| 56 | 2RIA | Ring Indicator, CHA2, RS-232 | input |
| 57 | GND_2 | CHB1 ground | |
| 58 | 2DSRB | Data Set Ready, CHB2, RS-232 | input |
| 59 | 2DCDB | Data Carrier Detect, CHB2, RS-232 | input |
| 60 | 2DTRB | Data Terminal Ready, CHB2, RS-232 | output |
| 61 | 2RIB | Ring Indicator, CHB2, RS-232 | input |
| 62 | GND_1 | CHA1 ground | - |
Notes
The 62-pin connector carries signals for four serial channels. Channels 1 (CHA1, CHB1) provide both RS-232C control lines and RS-422 differential transmit/receive data and clock pairs; channels 2 (CHA2, CHB2) carry RS-232C signals only, including modem-control lines and separate transmit and receive clocks. The X.21 control and indication differential pairs (+CA1F/-CA1F, +CB1F/-CB1F, +IA1/-IA1, 1DCDA/-IA1, 1DCDB/-IB1) on channels 1 indicate dual-mode operation supporting both RS-232C and X.21 interface standards. Multiple dedicated ground pins (GND_1 through GND_6) are distributed across the connector to reduce crosstalk between channel pairs.
Signals
- +CA1F / -CA1F — X.21 differential control output pair for channel CHA1.
- 232TXDA1 / 232TXDB1 — RS-232C transmit data outputs for channels CHA1 and CHB1 respectively.
- 1RTSA / 1RTSB — RS-232C Ready To Send outputs for channels CHA1 and CHB1.
- 1CTSA / 1CTSB — RS-232C Clear To Send inputs for channels CHA1 and CHB1.
- +CB1F / -CB1F — X.21 differential control output pair for channel CHB1.
- +1B1 — X.21 positive indication input for channel CHB1.
- 232TXDA2 / 232TXDB2 — RS-232C transmit data outputs for channels CHA2 and CHB2.
- 2RXDA / 2RXDB — RS-232C receive data inputs for channels CHA2 and CHB2.
- 2RTSA / 2RTSB — RS-232C Ready To Send outputs for channels CHA2 and CHB2.
- 2CTSA / 2CTSB — RS-232C Clear To Send inputs for channels CHA2 and CHB2.
- +IA1 — X.21 positive indication input for channel CHA1.
- +422TXCA1 / -422TXCA1 — RS-422 differential transmit clock inputs for channel CHA1.
- +422RXDA1 / -422RXDA1 — RS-422 differential receive data inputs for channel CHA1.
- +422RXCA1 / -422RXCA1 — RS-422 differential receive clock inputs for channel CHA1.
- +422TXDA1 / -422TXDA1 — RS-422 differential transmit data outputs for channel CHA1.
- +422TXCB1 / -422TXCB1 — RS-422 differential transmit clock inputs for channel CHB1.
- +422RXDB1 / -422RXDB1 — RS-422 differential receive data inputs for channel CHB1.
- +422RXCB1 / -422RXCB1 — RS-422 differential receive clock inputs for channel CHB1.
- +422TXDB1 / -422TXDB1 — RS-422 differential transmit data outputs for channel CHB1.
- 2TXCA / 2TXCB — RS-232C transmit clock inputs for channels CHA2 and CHB2.
- 2RXCA / 2RXCB — RS-232C receive clock inputs for channels CHA2 and CHB2.
- 1DSRA / 1DSRB — RS-232C Data Set Ready inputs for channels CHA1 and CHB1.
- 1DCDA/-IA1 — RS-232C Data Carrier Detect / X.21 negative indication input for channel CHA1.
- 1DTRA / 1DTRB — RS-232C Data Terminal Ready outputs for channels CHA1 and CHB1.
- 1RIA / 1RIB — RS-232C Ring Indicator inputs for channels CHA1 and CHB1.
- 1DCDB/-IB1 — RS-232C Data Carrier Detect / X.21 negative indication input for channel CHB1.
- 2DSRA / 2DSRB — RS-232C Data Set Ready inputs for channels CHA2 and CHB2.
- 2DCDA / 2DCDB — RS-232C Data Carrier Detect inputs for channels CHA2 and CHB2.
- 2DTRA / 2DTRB — RS-232C Data Terminal Ready outputs for channels CHA2 and CHB2.
- 2RIA / 2RIB — RS-232C Ring Indicator inputs for channels CHA2 and CHB2.
- GND_1 – GND_6 — Dedicated ground returns distributed across the connector to isolate channel pairs.