Rockwell Automation 1799-DASCII DeviceNet Serial Interface - Manual (Page 22)

22 DeviceNet Serial Interface Module
Publication 1799-IN012B-EN-P - July 2008
sent to the master. If the 1799-DASCII module receives a character while the buffer
is full, it internally generates an overflow error in the status byte.
The subsequent received characters are received into the buffer and handled as the
start of the next incoming message string.
Set Up and Using Delimiter Operation (parameters 5, 6, 7, 8)
When receiving data strings from the serial device, the 1799-DASCII module can
take advantage of Start and Stop (End) delimiters. The Start Delimiter is the
start-of-string indicator and the End Delimiter is the end-of-string indicator. This lets
explicit control over which characters are sent to the master.
When Start Delimiter operation is selected, a character must be defined that
prompts the 1799-DASCII module to start storing the incoming data string. All
characters up to this Start Delimiter (after the previous message was completed) are
ignored. Once the Start Delimiter is received, all characters are stored until the End
Delimiter is received or the Max Receive Char Length is reached (or the RX
Time-out time is exceeded, if that option is selected). Once the End Delimiter is
reached, the data string is captured and prepared to send to the DeviceNet master.
If either delimiter is used, you can also elect whether to include those characters in
the string sent to the master. The Start Delimiter mode parameter is 5, the Delimiter
character is 6. The End Delimiter mode is parameter 7 and the End Delimiter
character is 8.
Rx Message Time-out (parameter 9)
The 1799-DASCII module has a receive time-out value configurable in 1 ms
increments. When this value is non-zero, the module's timeout counter resets on
the receipt of each new byte of data. If the timeout counter expires, the module
sets the nondelimited flag in the Status Byte and updates the Produce buffer with
the current data string.
ATTENTION
Incoming characters could be missed in the process of handling a string longer than the
defined max length.
This value can be set and retrieved by EDS parameter 4.
Message Time-out Values
Value Time-out Action
0 Disabled
1…65,535 Time-out time in milliseconds (ms)