Rockwell Automation D17846.2.4 CONTROLNET KT EMULA - Manual (Page 23)

Publication 1784-6.2.4 - September 1997
How Your Driver Operates the KTCX Card 3-3
Important: The mailbox is in an invalid state if both the Access
Request and the Data Valid bytes show opposing values (one shows
00h and the other 01h).
Reading and Writing Access Request and Data Valid Flags.
The order in which you read these flags must be as follows.
To read access request and data valid flags:
1. Read the Access Request byte (0080h for sending or 0480h for
receiving).
2. Read the Data Valid byte (0081h for sending or 0481h for
receiving).
The order in which you write these flags must be as follows.
To write access request and data valid flags:
1. Write the Data Valid byte (0081h for sending or 0481h for
receiving).
2. Write the Access Request byte (0080h for sending or 0480h for
receiving).
General Packet Structure The general form of PCCC message packets is a combination of
protocol command, and data bytes:
• Protocol bytes make sure that the packet gets to its destination,
handling routing, error checking, and error recovery. The
protocol bytes are the set of instructions and data that the protocol
layer returns. This layer is emulated by the KTCX card.
• PLC commands and transaction identification control the PLC
and provide a serialized means of tracking packets.
• Data bytes contain the information from the application or PLC.
For more information on the contents of the PCCC message packet,
refer to the DF1 Protocol and Command Set (Pub. 1770-6.5.16).
Refer to table 3.A to see the structure of a typical packet.
Table 3.A Typical Packet Structure
Protocol Bytes
Command and ID Bytes
Packet Data Bytes
PLC Commands
Transaction ID
Application Data