Advanced Energy HFV 8000, User Manual

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5705211-C Communication Interfaces 4-15
HFV 8000 Generator
If the value specified in the length bits (bits 0, 1, and 2) of the Header field is 0 to 6,
the HFV generator expects 0 to 6 data bytes. However, if the value in the Header field
is 7 (07h), the HFV generator looks for the Optional Length byte after the Command
field and reads this value to calculate the data byte count.
AE BUS CHECKSUM BYTE
This one-byte field is the last byte in the packet. The value of this byte depends upon
the number of bytes in each of the preceding fields. The transmitting unit determines
this value by accumulating the
exclusive-or (XOR) of all bytes of the packet up to, but
not including, the checksum value. The receiving unit accumulates the XOR of all
bytes of the packet, including the checksum. If the result is zero, the unit has received
the packet intact.
The unit will act on the message only if the address is valid and the checksum is
validated as having no parity errors.
Creating an Ideal Communications Transaction
Figure 4-10 illustrates the steps in an ideal communications transaction between a host
computer and the HFV generator.
Figure 4-10. AE Bus communications transaction
Host HFV generator