ICP DAS USA I-7521 User Manual page 93

What is "synchronized sampling? "
The host computer can only send one command string at a time. If there are
two modules, the host computer must send and receive the commands from
module 1 then the commands from module 2 in response, so there is a time
delay between the two commands. The "synchronized sampling" command is
designed for all input modules. When the synchronized sampling command
#**[CrLf] is received, all input modules on theRS-485 network will perform
the input function at the same time and store the values into the intend
memory of the module. The host computer can then send a read
synchronized data command $AA4 to read the data separately.
I-7521/I-7522/I-7522A/I-7523/I-7524/I-7527 User's Manual,Ver2.5 Aug.2015
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