Comtrol UP DeviceMaster User Guide - Manual (Page 30)

30 - Chapter 2. Programming Interface DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I
Instance Attribute Definitions
2.3.2.4. Instance Attribute Definitions
Attribute Description
Attribute 1
Transmit (PLC to
DeviceMaster UP)
Message Data
This attribute transmits data out of a serial 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 serial port
packet received.
• A length of zero indicates no data was received on the specified serial port.
• Two or more Gets may return the same data packet, but the messages will also
have the same sequence number.
• Serial packets up to 1518 bytes may be received while operating in the Write-To-
Tag or Write-To-Tag-Synced receive methods. For serial 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 be 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 serial 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 serial 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.