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Universal Desktop Box Serial Y CableAll Universal Desktop Boxes
are equipped with two 16550A compatible serial interfaces with full modem
control, unfortunately due to the compact packaging of the UDB there is
insufficient space available to incorporate two serial port sockets on the rear
of the system. The Digital solution to this problem is to provide a single male
DB25 socket with two sets of signals present.
The first Port A is presented on the standard RS-232 pins, the second Port B
is presented on pins that are normally unused by the RS-232 standard. A special
Y Cable is available from Digital that splits these signals onto two sockets
with standard pinouts. The part number for this cable is B25X-1F (17-04047-01
A01) Should you wish to make your own cable, or need other connections the
pinout of the male DB25 socket on the UDB is as follows. Note that pin 7 GND is
shared between Port A and Port B. Pins are counted right to left with pin 1 top
right as you look into the connector with pins pointing out at you, pin 14 is
below pin 1
Pin Signal
2   Port A TXD
3   Port A RXD
4   Port A RTS
5   Port A CTS
6   Port A DSR
7   Port A GND
8   Port A DCD
20  Port A DTR
22  Port A RI
7   Port B GND
11  Port B DTR
12  Port B DCD
13  Port B CTS
14  Port B TXD
16  Port B RXD
19  Port B RTS
23  Port B DSR
25  Port B RI
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