Specifications

CHAPTER 1
Introduction
14 Serial I/O Ports
Figure 1-6 Serial port sockets
The extra pin on the modem connector provides +5V power from the ADB power supply.
A modem should draw no more than 100 mA from that pin. The total current available
for all devices connected to the +5V supply for the ADB and the modem port is 500 mA.
Both serial ports include the GPi (general-purpose input) signal on pin 7. The GPi signal
for each port connects to the corresponding data carrier detect input on the SCC (Serial
Communications Controller). On serial port A (the modem port), the GPi line can be
connected to the receive/transmit clock (RTxCA) signal on the SCC. That connection
supports devices that provide separate transmit and receive data clocks, such as
synchronous modems. For more information about the serial ports, see Guide to the
Macintosh Family Hardware, second edition.
Table 1-4 Serial port signals
Pin
number Signal description
1 Handshake output
2 Handshake input
3 Transmit data –
4 Ground
5 Receive data –
6 Transmit data +
7 General-purpose input
8 Receive data +
9 +5 volts (modem port only)
Printer Modem
8 7
1
5 4
2
39
8 7 6
1
5 4
2
3
6