User`s manual

Western Reserve Controls, Inc. 1782-JDC User’s Manual
21
5.1.4 Setting up the Data Frame Format
The data frame format parameter defines the size of the data frame that is transmitted and
received over the serial link. This parameter defines the number of data bits per character (7
or 8), the parity (odd, even or none) and the number of stop bits (1 or 2). The JDC provides
several options that can be used to match the choice(s) available with your ASCII device, as
the setting on both the JDC and your ASCII device must match exactly.
These values can be set and retrieved by using the standard set and get services on class 15
(F
hex
), instance 1, attribute 1 (See Table 5-1).
5.1.5 Setting up the Receive Character Buffer Length
The receive character buffer length is the number of characters that the JDC can receive from
your ASCII device into its buffer before generating an overflow and forcing the data into the
JDC DeviceNet transmit buffer. This size value also determines the maximum size of the poll
response to the Master from the JDC and is determined by:
produce_size = receive_character_length + 3
The valid settings for this value are 0-124. The default value is 20 (14
hex
). This produce_size
is used to set up the Poll, Cyclic and/or COS receive (response) sizes at your Master device.
These values can be set and retrieved by using the standard set and get services on class 15
(F
hex
), instance 5, attribute 1 (See Table 5-1).
5.1.6 Setting up the Transmit Character Buffer Length
The Transmit character buffer length is the number of characters that the JDC can receive in
its transmit buffer from the DeviceNet system. This size value also determines the maximum
size of the poll command to the JDC from the Master (which is the JDC’s Consume Size) and
is determined by:
consume_size = transmit_character_length + 2
The valid settings for this value are 0-124. The default value is 20 (14
hex
). This consume_size
is used to set up the Poll transmit (command) size at your Master device.
These values can be set and retrieved by using the standard set and get services on class 15
(F
hex
), instance 6, attribute 1 (See Table 5-1).
5.1.7 Setting up the Pad Mode
Pad Mode operation is the method by which the JDC adds extra characters to the end of its
received data string (after the delimiter char) from the external ASCII 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 always a constant length, and that length is the
number specified in the receive_character_length parameter plus 3. The quantity of pad
characters sent can vary from message to message, depending upon the size of the incoming
string.
Pad mode is included with our device for compatibility with scanners that to not fully conform
to the ODVA specification for receiving variable length I/O messages. (Notable examples
include many Allen-Bradley’s scanners at the time of printing). For scanners with this
restriction, you must turn ON Pad mode (a value of 1). Turning Pad mode on will not harm
ODVA compliant scanners; thus the default value for pad mode is OFF. If your scanner
supports variable I/O messaging lengths, you may turn off pad mode off (a value of 0) to
conserve some network bandwidth.