13
Two lamps are fitted to the rear panel immediately below the GPIB connector, to assist in
diagnosing any GPIB communication problems. The RED lamp lights whenever the ILM is
addressed to TALK and the GREEN lamp lights whenever it is addressed to LISTEN. The
behaviour of the lamps is very dependent on the GPIB monitor in use. Some controllers
un-address an instrument at the end of any transaction, in which case the lamps will just
blink on for each transaction. Others leave instruments addressed between transactions
in which case one or other lamp may remain lit depending on whether ILM was last
addressed to talk or to listen.
Before any communication can occur, ILM must be given a unique GPIB address. By
default, ILM is supplied with its address set to 24. If this address is already in use by
another instrument on the bus, it can be changed from the front panel via the Test
Mode. This is described in section 9.5.
3.11
The GPIB to ISOBUS Gateway
An ILM fitted with a GPIB interface has the ability to act as a GATEWAY to an ISOBUS
cable, allowing other instruments to be linked to the GPIB without themselves requiring
GPIB interfaces. This can enable other Oxford Instruments products, for which an internal
GPIB interface is not available, to be linked. It offers the additional advantage of optical
isolation between these instruments and the GPIB.
To use the gateway, all that is required is GATEWAY MASTER ADAPTOR. This allows the
25 way ISOBUS MASTER socket to be linked to the 25 way RS232 socket on the ILM. The
adapter is a symmetrical 25-way plug to 25-way plug link, with pin connections as shown
below.
Beware of using 25-way plug to 25-way plug adapters, sold as "DCE-linkers" by some
suppliers. Several different conventions exist for these, not all of which will work as a
Gateway Master Adapter. The connections required are given in the table below. A
Gateway Master Adapter providing these connections may be obtained from Oxford
Instruments.
25 WAY PLUG
25 WAY PLUG
1
1
2
3
3
2
7
7
6
4
4
6
Note that the connections are symmetrical and the adapter may be plugged in either way
round.
The necessary protocols for use as a Gateway Master are included as standard in ILM and
are described in section 6.6.9.
