GDU
27-1500
Original Instructions
11
9901X0265 Issue 2
2.6
Computer Communications Interfaces
The GDU is currently pplied with an RS232 interface for communication with the host
computer. The interface connector is located on the rear panel of the GDU. The
connection is a 9 way D fixed plug for the RS232 interface. A separate Ethernet
connection is available which may be used as an alternative to the RS232 link.
Before connecting the GDU to the computer system it is recommended that the
following precautions be observed:
All peripheral devices should be turned off
Plug each peripheral and the host into the mains supply
All devices must have their grounds connected to the mains earth.
2.7
Configuring the RS232 Interface
The RS232 interface does not need configuring as it has a fixed baud rate/protocol.
The host computer must be able to support the following configuration.
2.7.1 Baud Rates and Word Formats
The rate at which devices can communicate is specified by a “Baud rate” or the number
of BITS/second. It is important that both transmitting and receiving devices operate at
the same rate. Data is transmitted as a burst of pulses comprising an initial START
BIT, followed by a number of BITS that constitutes a word.
Baud rate is 9600, Word size is 8 BITS with no PARITY check, and finally 1 STOP BIT.
2.7.2 XON/XOFF Protocol
This legacy mode where the host has no “listen” or input buffer for temporarily storing
data, eg. Apple or Hewlett Packard microcomputers, is not supported.
2.7.3 RS232 Interface Connections
The standard 9
way ‘D’ RS232 interface connector is located on the GDU rear panel
and has the following pin connections:
Pin
Signal
1
Protective Earth
2
TxD (from GDU)
3
RxD (to GDU)
4
Not connected
5
Signal 0v
6
Not connected
7
Not connected
8
Not connected
9
Not connected
Table 1 RS232 Interface Connections
