Rockwell Automation 1799-DASCII DeviceNet Serial Interface - Manual (Page 31)

DeviceNet Serial Interface Module 31
Publication 1799-IN012B-EN-P - July 2008
Transmitting Serial Data
The length of the string set determines the use of a delimiter in transmitting data to
a serial device from the 1799-DASCII module.
If the string length is zero, or the data type is type Array, the following happens:
•
The 1799-DASCII module receives data sent from the DeviceNet master and uses the End Delimiter to
determine how much data is sent to the serial device. The 1799-DASCII module computes the length
and stores this as the new length in the string attribute. (This does not appear if the data type is array.
You see the string truncated and the length is in the background.)
•
If a delimiter is contained within the string, all characters in the data field up to and including the
defined delimiter are stored.
•
If no delimiter is contained within the string, the 1799-DASCII module stores the data in the data field
received.
If the string length > 0 or the data type is String or Short_String, the following
happens:
•
The 1799-DASCII receives data sent from the DeviceNet master, ignoring any embedded terminator. It
stores the number of characters defined in Max_Number_of_Transmit_Chars, or the total sent by the
master, whichever is less.
Now, the 1799-DASCII sends the data immediately if attribute X is set to 1. You can
cause this data to be transmitted by incrementing the record counter.
The following identifies which parameters transmit serial data to the ASCII device:
•
Explicit Messages to Transmit Serial Data String
•
Parameters 26, 27, and 28 can be used to set up the serial data string and send it to the ASCII device
via the Explicit Messaging technique
•
Parameter 26 holds the data to be sent
•
Parameter 27 defines the size, in bytes, of the DeviceNet message to be sent from the 1799-DASCII
module to the device
•
Parameter 28 holds the record number of the data string in parameter 24 if the Header option is
selected. Changing the record causes the data in parameter 24 to be transmitted immediately from the
master to the 1799-DASCII module