Comtrol UP DeviceMaster User Guide - Manual (Page 49)

DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I Chapter 2. Programming Interface - 49
Instance Attribute Definitions
2.3.5.4. Instance Attribute Definitions
Attribute Description
Attribute 1
Transmit (PLC to
DeviceMaster UP)
Message Data
This attribute transmits data out of a socket port on the DeviceMaster UP.
In most cases, incrementing the sequence number is optional. However, it is
required if you enable the Transmit Sequence Number Checking option. (For
more information, see Attribute 16 - Serial Port Transfer Options on Page 22.)
The length must be at least one and a maximum of 440-bytes.
A Get returns the last successfully transmitted data message.
Attribute 2
Receive (DeviceMaster
UP to PLC) Message Data
This attribute provides the receive data while operating in the Polling
communication method.
• DeviceMaster UP increments the sequence number for each new socket port
packet received.
• A length of zero indicates no data was received on the specified socket port.
• Two or more Gets may return the same data packet, but the messages will
also have the same sequence number.
• Socket packets up to 2048 bytes may be received while operating in the
Write-To-Tag or Write-To-Tag-Synced receive methods. For socket packets
over 440 bytes, the DeviceMaster UP places the data into a sequence of tags.
These tags must meet the following criteria:
- All must be of type SINTs.
- The entire sequence must be large enough to contain the maximum sized
receive packet plus four SINTS for the sequence number and length
parameters.
- All tags except the last of the sequence must be 444 SINTs in size.
- The tags must have the same base name and numbered in sequence. The
first tag is not numbered (i.e. Com1_RxData), the second tag has a 2
appended (i.e. Com1_RxData2), the third has a 3 appended (i.e.
Com1_RxData3) and so on.
- The sequence number and total length is placed in the first tag and the
first tag is the last tag updated. Therefore, once the sequence number is
updated, the entire socket packet has been received and the PLC can
process the data.
Attribute 3
Receive (DeviceMaster
UP to PLC) Produced
Data Sequence Number
Use this attribute to get and set the Produced Data Sequence number. This is the
same Produced Data Sequence number sent to the PLC in all the receive
communication methods.
Attribute 4
Receive (DeviceMaster
UP to PLC) Consumed
Data Sequence Number
Use this attribute to get and set the Consumed Data Sequence number. You can
only specify this attribute when you are using the Unsolicited - Write-to-Tag-
Synced receive method under Attribute 17 in the Serial Port Configuration object
definition. When used, the PLC increments this attribute to indicate the data
received has been consumed and it is now ready for another socket data packet.
For more information, see the description of Unsolicited -Write-to-Tag-Synced in
Attribute 17 on Page 22.
Attribute 5
Transmit (PLC to
DeviceMaster UP)
Produced Data Sequence
Number
Use this attribute to get and set the Transmit Produced Data Sequence number.
This is the same Produced Data Sequence number sent to the DeviceMaster UP
in the Transmit Message data.