Rockwell Automation 1799-DASCII DeviceNet Serial Interface - Manual (Page 24)

24 DeviceNet Serial Interface Module
Publication 1799-IN012B-EN-P - July 2008
Set Up and Use Pad Mode (parameters 11 and 12)
Pad mode operation is the method used by
the 1799-DASCII module to add extra
characters to the end of its received data
string (after the delimiter character) from the
external I/O device before sending the string
to the DeviceNet scanner (master) as an I/O Response. The quantity added is such
that the data string returned to the scanner is a constant length, and that length is
the number specified in the Receive Character Length parameter, plus any header
options. The quantity of pad characters sent can vary from message to message,
depending on the size of the incoming string.
Pad Mode Selection (parameter 11)
Pad mode is included for compatibility with scanners that cannot receive variable
length I/O messages. For such scanners, you must turn on Pad mode (a value of 1).
Turning Pad mode on does not harm scanners that do support variable length
receive messages. The default value for Pad mode is off. If the scanner does
support variable I/O messaging lengths, the Pad mode option can be set to off (a
value of 0) to conserve some network bandwidth.
The selection of Pad mode is valid only for the DeviceNet message that the
1799-DASCII produces. It has no effect on DeviceNet messages sent from the
scanner to the 1799-DASCII module. This value can be set and retrieved by using
the standard set and get services on Use parameter 11 of Table 4.
Pad Mode Character (parameter 12)
You can specify the character that Pad mode uses to pad the received serial data.
This can be set to any valid I/O value (0…127 in 7-bit modes, 0…255 in 8-bit
modes). This value can be set and retrieved by using the standard set/get services
on parameter 12. See the EDS Parameters table starting on page 12.
Produce Data DeviceNet Format - String_String Type
Byte 1 Byte 2 Byte 3 Byte 4 Byte 5-X (250 bytes max)
Transaction ID Status byte Reserved Length ASCII data (including optional <terminator>.
Produce Data DeviceNet Format - String String Type
Byte 1 Byte 2 Byte 3 Byte 4 Byte 5-X (250 bytes max)
Transaction ID Status byte Length (low byte) Length (high byte) ASCII data (including optional
<terminator>.