Rockwell Automation 1755-OF8 GuardPLC Controller Systems - Manual (Page 270)

270 Publication 1753-UM001C-EN-P - March 2010
Chapter 21 Communicate with ASCII Devices
ASCII Protocol The controller is a slave ASCII device and expects this protocol from
the master device.
ASCII Master - Request
If the ASCII master sends a request, the slave can send a response.
The master request has this format (each character is one byte).
TIP
The offset in the ASCII output section is numbered based on bytes. In the example, the first signal uses
bytes 0, 1, 2, and 3. The second signal uses bytes 4 and 5. However, when you request these signals in
the command string (see
ASCII Master - Request below), the first signal is always 0, the second signal
is always 1, the third signal is always 2, and so forth.
The output section automatically sorts the name field based on alphanumerical order. This does not
automatically change the offsets, but if you renumber after sorting, the offsets will change and there is
no undo feature. This changes the order in which the signals are sent out the serial port.
Because names are used only in printouts, you may want to enter these names in alphanumeric order
to begin with. (For example signal 101, signal 102, signal 103, signal 104, and so forth.)
Start Sign Destination Source Function Code Start Address Number of
Variables End Sign
1 char 2 char 2 char 1 char 5 char 3 char 1 char
Component Description
Start Sign identifies the start of a message
^ character
Destination unique slave address (GuardPLC controller)
01…99
Source unique master address (requester)
01…99
Function Code read data
R character
Start Address data start address for characters to read (offset)
00000…65535
Number of Variables number of variables to read and send back to master
000…999
End Sign identifies the end of a message
& character