Displayless 146 Unit Cha
ter Three: Overview
100
How To Establish RS-232 Communications
Connect the RS-232 source to a displayless 146 unit with the correct RS-232 cable. Install the
146 unit into your system using the rear panel connector. Note that the RS-232 cable used for
rear panel communications (refer to Table 32, page 77, for the proper MKS part number) differs
from the RS-232 cable for front panel communications (MKS p/n CB146-21). All RS-232
commands are supported through either connector. Refer to
Chapter Nine: RS-232
Communications
, page 255, for a complete list of RS-232 commands/requests and the proper
protocol for communications.
Refer to Table 32, page 77, for a pinout of the rear panel RS-232 connector. Table 30, page 75,
lists the pinout of the front panel Interface connector.
Pins 1 through 5, 7, 8, and 20 on a displayless unit’s front panel are involved with RS-232
communications. Pins 4 and 8 are especially worth noting. If pin 4 is left open, the device
connected to the 146 unit can only receive RS-232 communications that are currently being
issued
from
the 146 unit, through the rear panel. For example, if a status query is sent to the 146
displayless unit, the reply (which includes the header identifying the query), is received. If pin 4
is grounded, the device connected to the 146 instrument overrides the rear panel communication
link and it can communicate fully with the 146 unit (that is, it can initiate queries).
Pin 8 can supply a +5V signal, which can be used to power one of several types of remote
terminals.
The functions on pins 5 and 20 are special options that must be specifically requested from the
factory.
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