General Information
Chapter Nine: RS-232 Communications
258
General Guidelines for RS-232 Messages
•
All commands are sent and received as ASCII strings except for the checksum, which is
binary.
•
All commands must include a parameter byte, even if it has no significance. Any
character, including a space, can be supplied in its place.
•
The checksum bytes are ignored, unless the checksum mode is enabled.
The checksum is the sum of all the ASCII values in the message. It includes everything
preceding it, beginning with the “at” character (@), and ending with the carriage return
(CR). The checksum command needs no checksum value of its own. If the checksum is
enabled, the 146 unit expects a checksum for all commands and returns a proper
checksum. The checksum is sent with the low byte first. The number of data bits must be
set to 8 when the checksum is enabled. The 146 unit is initially configured with the
checksum disabled. Refer to Miscellaneous Messages, page 273, to enable the checksum.
•
UPPERCASE letters must be used in all command messages.
•
Floating point data fields may be entered in either scientific notation or fixed notation.
For example, to set the disconnect threshold to 1 x 10
-10
on channel 1, the 146 instrument
accepts either of the following commands:
a)
@0651:.0000000001<CR>
b)
@0651:1E-10<CR>
where:
<CR>
is a carriage return
Also, it is possible to specify the form that all RS-232 responses (from the 146 unit) are in, by
sending the following command:
@508x:<option><CR>
where:
x
is anything
<option> is E (for scientific notation) or D (for fixed notation)
<CR>
is a carriage return
Note
This command is not saved at power down and must be re-initialized
after each power up.
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