Rockwell Automation 1734-485ASC POINT I/O ASCII User Manual - Manual (Page 53)

Publication 1734-UM009B-EN-P - July 2003
Configuring Your ASCII Module 2-27
Produce Immediate vs. Master/Slave Handshake Mode
Selecting the mode option defines when the ASCII module sends new
data to the DeviceNet Master (produces new data on DeviceNet).
In Produce Immediate mode (default), there is no gating by the
ASCII module of data sent from the ASCII module to the DeviceNet
Master. The module sends its most current serial port data to the
Master in response to each Poll command or explicit message, or in
response to a COS or Cyclic event. It is the Master’s responsibility to
be ready to accept and process new data strings as they are received.
In Master/Slave Handshake mode, the ASCII module refrains from
updating the new ASCII data until the Master requests it. This
technique is useful when the Master needs to ensure that some
specific actions have taken place before receiving the new serial data.
When Master/Slave Handshake mode is active, two data fields in the
message headers are used to initiate and complete the transaction:
· The New Data Available Flag is set in the serial status byte of
the ASCII Poll response message.
This informs the Master that a new data string has been received
and the module is waiting for the OK from the Master to send it.
· The Next RX ID byte is updated by the Master to the ASCII
module that it is now ready to receive the new data string.
IMPORTANT
Master/Slave Handshake mode is only available if
the Transmit Immediate mode is also active.
Table 2.11 ASCII Modules Consume Assembly Message with Handshake Mode (Short_String)
Byte 1 Byte 2 Byte 3 Byte 4 Byte 5-X Byte X+1
(Max = 132)
Next RX ID Byte
(Handshake Mode
Only)
Transaction ID Byte Reserved Length ASCII Data
(max 128 bytes)
End of String
Delimiter or Last
Data Byte