Apple 640 manual Using PC peripheral devices, TXDA+ GP1 RXD+

Using PC peripheral devices

Because of the RS-422 implementation of the Macintosh, the following

RS-232 signals are not available to the PC:

mCarrier Detect (CD)

mData Set Ready (DSR)

mRequest to Send (RTS)

mRing Indicator (RI)

Applications or peripheral devices requiring these signals won’t work with your DOS-compatible Macintosh.

While the DOS-compatible Macintosh does not support Carrier Detect (CD) signals, you can set most communications application programs to respond to the CARRIER string sent back by most modems.

For more information about using serial ports from DOS, see the documentation that came with your DOS software.

IMPORTANT The following chart lists the various signals present on the Macintosh Mini DIN-8 connector, and on what pins these signals are present on PC-style DB-9 and DB-25 connectors. This information may be of use if you are planning to have a custom cable built. Refer to the manual for the peripheral device that you plan to attach to the Macintosh for the recommended serial connection, and use the following chart to find out what the proper Macintosh wiring should be.

Macintosh signal	Macintosh Mini DIN-8	DB-9	DB-25	RS-232 name
HSK0	1	4	20	DTR
HSK1	2	8	5, 8	CTS, DCD
TXD-	3	3	2	TXD
GND	4	5	7	GND
RXDA-	5	2	3	RXD
TXDA+	6	N/C	N/C
GP1	7	N/C	N/C
RXD+	8	5	7	GND

Operating in the PC Environment 61