5702269-C I/O Communication and Control 4-57
Pinnacle™ Plus+ 10 kW
• A command that requests data or status information
• A command and data that change a parameter setting
• An executable command
Once the Pinnacle Plus+ unit receives the message packet, the Pinnacle Plus+ unit
verifies that the message is intended for it and not for another unit in the network. At
this time, the Pinnacle Plus+ unit also analyzes the checksum to verify that the
message was received correctly.
If the address does not match, the Pinnacle Plus+ unit does not respond to the host; the
Pinnacle Plus+ unit resets and resumes waiting for a message addressed to it. If the
address is correct but the exclusive-or sum of the bytes in the packet (including the
checksum) is not zero, the Pinnacle Plus+ unit sends a NAK (negative
acknowledgment, hex code 15h) to the host. If the address matches and the message is
intact, the Pinnacle Plus+ unit sends an ACK (acknowledgment, hex code 06h) to the
host.
If the Pinnacle Plus+ unit receives a request for data or status information, it gathers
and sends the requested information. Otherwise, it evaluates the incoming command
and sends a message-packet that contains a 1-byte data value (CSR code) to the host (
see “Understanding Command Status Response (CSR) Codes” on page -57 ). CSR
code 0 is sent when the command has been accepted.
If the host receives a NAK from the Pinnacle Plus+ unit, the host either re-transmits
the packet or does whatever else it has been programmed to do in this situation. If the
host receives an ACK, it waits for the requested data or status information or for the
CSR code telling it whether or not the new parameter was accepted. If the host
receives no response within a reasonable period, it takes whatever action it has been
programmed to take.
Meanwhile, the Pinnacle Plus+ unit has prepared a message packet with the requested
information or appropriate CSR code, which it then transmits to the host. The host
determines by means of the checksum if the message is complete. If the host detects
an error in the transmission (by using the Checksum), it can request the packet be sent
again by transmitting a NAK.
If the Pinnacle Plus+ unit receives an ACK, it returns to the normal waiting state. If
the Pinnacle Plus+ unit receives a NAK, it re-transmits the message packet. The
Pinnacle Plus+ unit continues to re-transmit in response to NAK transmissions until
the host stops the cycle. If the Pinnacle Plus+ unit receives no response, it assumes an
ACK and returns to the waiting state.
Understanding Command Status Response (CSR) Codes
When the Pinnacle Plus+ unit sends a Command Status Response (CSR) code in
response to a command, interpret the CSR (a one-byte response) code in the following
way:
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