Delta OHM HD2817T Series, Manual

Page: 49 / 64

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18. Appendix – The communication protocol
The communication parameters are common to all RS232 and RS485 ports and are:
Baud rate: 9600 Baud,
Parity: None,
Data bits: 8,
Stop bits: 2,
Protocol: Xon-Xoff.
The serial command “KBH” allows setting the Baud rate to 57600. This choice is not
permanent, upon the next power on the Baud rate is restored to 9600.
Each command sent to the instrument is preceded by the address string AxxZ, where xx is the
address assigned to the instrument, and terminated by the Carriage Return (ASCII 0D).
When the AUX COM communication port is selected, the instrument replies to any address.
This way the communication through the AUX COM can occur without setting the instrument
address, for example always using the string A00Z.
The instrument only replies to commands and queries preceded by the correct address string.
For example, A01ZP0 is the “Ping” to which the instrument with the address 01 has to reply
with the confirmation character.
A confirmation character usually precedes the reply strings generated by the instrument (with
some exceptions).
The instrument response character is:
“&” when in normal mode,
“$” when in suspend mode,
“#” when in OFF-LINE mode.
For example, the command AxxZK1 receives back a string containing the performed
measurement. If the string is preceded by “$”, it means the instrument is sending an old
measurement, “frozen” at the moment of suspension. But some commands are not enabled or
effective in OFF-LINE mode (e.g. the command K1).
If the commands are not correctly addressed, no response is obtained.
The correctly addressed commands, but wrongly formulated or illegal, get back a “?”.
A detailed description of the connection to a PC is reported in the chapter “ Description of the
connection to a PC ”.
18.1. Permanent changes of the functioning mode
All commands requiring permanent changes of the functioning mode should be preceded by
the request to enable modifications “
AxxZYU ”, otherwise they will get back the rejection
character (“?”). This includes date and time setting, logging interval, etc.
The modification enablement expires after about 8 minutes. The enablement expiration is not
notified, but is renewed each time a next enablement serial command is sent. In case of
doubt, you can simply place the enablement string before the desired command.
Warning : to prevent the internal device managing serial communication from stopping, the
instrument resets it when the line is idle for two minutes .
It could happen that a command gets skipped because it occurred during reset. Due to this,
the communication protocol should provide for command reiteration before generating a fault
signal.
As the normal response latency does not exceed one second, the reiteration should occur after
a two-second timeout.
The querying of multiple instruments of a network can occur every second.