Rockwell Automation 1734-485ASC POINT I/O ASCII User Manual - Manual (Page 25)

Publication 1734-UM009B-EN-P - July 2003
Installing the ASCII Module 1-15
Produce Immediate vs. Master/Slave Handshake Option
This option defines when the ASCII module sends new data to the
DeviceNet Master (produces new data on DeviceNet).
In Produce Immediate mode (default), the ASCII module sends its
most current serial port data to the DeviceNet Master in response to
each Poll command or explicit message, or in response to a COS or
Cyclic event.
With Master/Slave Handshake active, the ASCII module keys on the
first byte (Next RX ID) of the Poll command or explicit message to
determine whether or not the new data from its serial port is sent to
the DeviceNet Master. This technique is useful when the Master needs
to ensure that some specific actions have taken place before receiving
the new serial data.
In this operating mode, the module sets the New Data Flag in its Serial
Status byte when a new string is received into the serial port. When
the Master is ready to receive the new data, it changes the value of the
Next RX ID byte in the next Poll command or explicit message. Upon
detection of the Next RX ID value change, the module updates its
produce buffer with the most recent serial input string.
Pad vs. No Pad Option
If the Pad option is selected (default), the ASCII module will always
send a fixed number of data bytes to the master. It is typically used
when a Terminating Character trigger is used to stop receiving ASCII
data. This is useful if the ASCII device connected to the ASCII module
has varying data lengths and the master cannot accept varying length
I/O messages. The ASCII module will fill a short message with the
pre-defined Pad Character. The data length is defined by the Max
Receive Length parameter.
If the No Pad option is selected, the ASCII module’s produce I/O
message will resize itself to the length of the received ASCII data. This
conserves bandwidth, but will cause scanners that do not support
variable I/O sizes to malfunction. Do not turn off Pad Mode if you do
not have (or do not know if you have) a scanner that supports
variable I/O sizes. Pad Mode is ON by default.