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DigiBoard Intelligent Serial Communications Boards
DB-25 Equipped Boards
Software Handshaking (XON/XOFF)
In most cases, serial terminals and printers need only a “three-wire” connection
to the board. All DigiBoard device driver software supports XON/XOFF
(software) handshaking, so the only signal lines necessary are Transmitted Data
(TxD), Received Data (RxD) and Signal Ground (SG). It may be necessary to
disable DCD (Data Carrier Detect) sensing through a software command—see
your DigiBoard device driver software manual for instructions. Cables must be
shielded to remain in compliance with FCC certification requirements, and the
shield should be connected to Chassis Ground (GND) at both ends of the cable
run.
A simple cable for connecting a terminal or a printer to a DB-25 equipped board
is shown in Figure 23.
Figure 23
Simple Terminal/Printer Cable (DB-25)
DB-25 Female
DB-25 Male
Pin
Pin
GND
TxD
RxD
RTS
CTS
DSR
SG
DCD
DTR
RI
GND
TxD
RxD
RTS
CTS
DSR
SG
DCD
DTR
RI
Signal
Shell
2
3
4
5
6
7
8
20
22
1
2
3
4
5
6
7
8
20
22
Signal
(
Cable Shield)
The cable shown in Figure 23 is a three-wire null modem cable—that is,
Transmitted Data on one end of the cable is connected to Received Data at the
other end, and vice versa.
The male DB-25 end can be plugged directly into most serial terminals and
printers without any adapters. The female DB-25 end plugs directly into one of
the DB-25 connectors on the fan out cable or connector box assembly.
