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9.4
P4 — Serial Port 1
Pin
Assigment
1
DCD (in)
2
DSR (spare in)
3
RXD (in)
4
RTS (spare out)
5
TXD (out)
6
CTS (in)
7
DTR (out)
8
SYNC/RI (in)
9
Ground
10
Not used
Pin 1 is at the top-left when holding the board with the battery to the bottom-
right.
The pin assignments are such that a 10-way ribbon cable (with the 10th core
removed) can connect a 10-way header to a DB-9 plug, and generate the stan-
dard PC/AT pin arrangement. This port is implemented as a Z180 port, which
does not support the DSR and RTS lines. These are therefore implemented us-
ing parallel port pins. This port can support synchronous modes, in which the
CPU's SYNC pin (normally used as the RI input) becomes an output. To pre-
vent contention with the RS232 receiver, the jumper at P5 should be removed
in synchronous working.
The Z180 uses the CTS and DCD pins as hardware enables. For the port to
operate, these must either be strapped to the DTR output, or connected via
(for example) a "null modem" cable to another PC-AT compatible port. If left
open, the port will be disabled.
9.5
P5 — SYNC Jumper
Pin
Assigment
1
From SYNC receiver
2
To SYNC pin on CPU
See P4 above. This link may be removed to prevent contention between the
SYNC output of the CPU chip, and the RS232 receiver output. The link should
be fitted in asynchronous operation, and removed for synchronous operation.
40
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