Allen-Bradley POINT I/O 1734-232ASC

Publication 1734-UM009A-EN-P - June 2002
Using the 1734-232ASC Module with the ControlLogix System Application Examples B-3
DeviceNet Data Details
With this example’s EDS configuration, the 1734-232ASC module takes
the maximum transmit and receive sizes from the EDS file and adds an
overhead of 4 bytes to each length. The data lengths in this example
are 20 bytes, so the TX and RX sizes for the scanner would be 24
bytes. The following table illustrates the format of the TX and RX data
with the header bytes.
Sending Data Through the 1734-232ASC Module
To send data from the master scanner through the 1734-232ASC
module, the desired data should be written into the data area, starting
at byte 5 after the header. Next, the number of bytes to be transmitted
should be put into byte 4 of the header. Lastly, the transaction ID byte
2 needs to be changed from it’s previous value to trigger the
transmission (i.e., incrementing the ID value by 1 each time a message
is to be sent).
Receiving Data From the 1734-232ASC Module
To receive data from the master scanner through the 1734-232ASC
module, look for the transaction ID in byte 1 to change in value.
When this happens, a new data buffer is available for storage. Read
the length of the data from byte 4 and copy that amount of bytes from
the data buffer starting at byte 5 into a file.
Table B.3 Receive Data Format - Short_String Data Type
Byte 1 Byte 2 Byte 3 Byte 4 Byte 5-X
(Max 128 Bytes)
Byte X+1
(Max = 132)
Transaction ID Byte Status Byte Reserved Length ASCII Data
(following the length
byte)
<CR>
(Terminator)
Table B.4 Transmit Data Format - Short_String Data Type
Byte 1 Byte 2 Byte 3 Byte 4 Byte 5-X
(Max 128 Bytes)
Byte X+1
(Max = 132)
RX ID Byte
(Handshaking Mode
only)
Transaction ID Byte Reserved Length ASCII Data
(following the length
byte)
<CR>
(Terminator)
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