Advanced Energy HFV 8000, User Manual

Page: 52 / 142

4-16 Communication Interfaces 5705211-C
Advanced Energy
®
T
0
: HOST TRANSMITS MESSAGE PACKET
The host computer sends a message packet to the HFV generator. The packet contains
one of the following:
• A command that requests data or status information
• A command and data that change a parameter setting
• An executable command
T
1
: UNIT VERIFIES HOST TRANSMISSION PACKET
Once the HFV generator receives the host computer transmission message packet, the
HFV generator verifies that the message is intended for it and not for another unit on
the network. At this time, the HFV generator also analyzes the checksum to verify that
the message was received correctly.
• If the address does not match, the HFV generator does not respond to the host
computer; the HFV generator resets and resumes waiting for a message addressed
to it. If the address matches but the
exclusive-or (XOR) sum of the bytes in the
packet (including the checksum) is not zero, the HFV generator sends a negative
acknowledgment (NAK), hexadecimal 15h, to the host computer.
• If the address matches and the message is intact, the HFV generator sends an
acknowledgment (ACK), hexadecimal 06h, to the host computer.
If the HFV generator 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 one-byte data value (CSR code) to the host (see
“AE Bus Command Status Response (CSR) Codes” on page 4-18 ). CSR code 0 is sent
when the command has been accepted.
If the host receives a NAK (15h) from the HFV generator, the host either retransmits
the packet or does whatever else it has been programmed to do in this situation. If the
host receives an ACK (06h), it waits for the requested data or status information, or it
waits 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.
T
2
: UNIT TRANSMITS RESPONSE TO HOST
The HFV generator prepares a response packet with the requested information or
appropriate CSR code, which it then transmits to the host computer. The host
computer then determines, by means of the checksum, if the response packet is
complete. If the host computer detects an error in the transmission (the checksum is
not validated), it can request the packet be sent again by transmitting a NAK (15h).