Chapter 8 - Appendices
8 - 10
584S Frequency Inverter
The symbols of this message are defined as follows:
(STX)
start of text character
(C1)(C2)
parameter specified by mnemonic
(D1 to DN)
parameter value
(ETX)
end of text character
(BCC)
Block Check Character (verification check digit which is again the exclusive OR of
(C1) to (ETX) inclusive and must be calculated by the computer before transmission)
Responses
Responses
Responses
Responses
After transmission of the whole message, the 584S responds to it by sending (ACK), (NAK) or by giving no reply.
1.
Positive acknowledgement (ACK)
When the 584S has received the message, it performs the following tasks:
a)
Checks for any parity errors in the message.
b)
verifies that the (BCC) character corresponds to the data pattern received.
c)
verifies that the (C1), (C2) command characters are a valid mnemonic that may be written to.
d)
verifies that the data (D1 to DN) is valid and not out-of-range*.
e)
updates the selected parameter with the new value contained in the message.
Only when all these tasks have been successfully completed does the 584S send the (ACK) response to the computer.
This signifies that the message was correctly received and implemented.
2.
Negative acknowledgement (NAK)
If the message fails any of the above checks, the 584S sends (NAK) response to the computer. This signifies that the
message received by the 584S contained an error and accordingly it has not updated the selected parameter. One
possible reason is the incorrect calculation of (BCC). At this point, the selected command may be repeated by sending
the data transfer string without re-establishing connection, until the (ACK) response is received by the computer.
* Data out-of-range returns NAK and is discarded.
3.
No Reply
Under certain circumstances, the computer may not receive a response from the 584S. This could be due to any of the
following reasons:
1.
Unit address identifiers not recognised.
2.
An error (e.g. parity) is found in one or more of the characters up to and including (BCC).
3.
Communications loop failure perhaps due to noise or wrong baud rate selected.
4.
Hardware failure.
In these cases the computer should be programmed to 'time-out', i.e. wait for a response for a short time (160ms minimum)
before trying again.
The sequence diagram for the data send function is given in Figure B.3.
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Summary of Contents for 584S
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