Figure 7-6. Ideal Communications Transaction - Advanced Energy MDX II User Manual

Figure 7-6. Ideal communications transaction

First, the host computer sends a message packet to the MDXII unit. 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
Once the MDXII unit receives the message packet, the MDXII unit verifies that the message is
intended for it and not for another unit in the network. At this time it also analyzes the
checksum to verify that the message was received correctly.
If the address is incorrect (that is, if the message was not intended for the MDXII unit that
received it), the MDXII unit does not respond to the host; the MDXII unit resets and resumes
waiting for a message addressed to it. If the address is correct but the sum of the bytes in the
packet (including the checksum) is not zero, the MDXII unit sends a negative
acknowledgment (NAK) with a hex code of 15h to the host. If the address is correct and the
message is intact, the MDXII unit sends an acknowledgment (ACK) with a hex code 06h to
the host.
5700262-R Serial Port Connection, Controls and Indicators
MDXII Power Supplies
7-11