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Serial Interface Operation
D374-20-880 Issue E
5 Serial Interface Operation
5.1 Message formats
Each message sent by your control equipment to the serial interface card must be a string of ASCII characters
terminated by a <CR> (carriage return character, ASCII code 13). You can include spaces in the messages to make
them more readable; the spaces are ignored by the serial interface card.
It is possible to send two types of message to the serial interface card and the first character of the message defines
the message type, as follows:
z If the first character is “?” (question mark), the message is a query. A query message causes a value (or
values) to be returned from the serial interface card. Query messages are described in Section 1.5.
z If the first character is a “!” (exclamation mark), the message is a command. Commands effect some action
on the TIC and then return a value to identify whether the command was valid or not. Command messages
are described in Section 1.5.
Messages that are sent to the serial interface card are queued in a buffer and then read and actioned by the serial
interface card one at a time. You can send the “/” character (ASCII code 47) to clear (empty) the buffer at any time;
any unactioned messages are ignored by the serial interface card.
Send the “/” character to reset the serial interface card before you start to send query and command messages.
Note: The serial interface protocol is case-sensitive. You must therefore use upper case text characters in serial
interface messages.
5.2 Reply messages
When the serial interface card receives a query or command message, it always sends a reply message to your control
equipment. A reply message is a string of ASCII characters terminated by the two control characters <CR><LF>
(carriage return and line feed, ASCII codes 13 and 10).
The content of a reply messages for a query message depends on the query message sent. If a query message is invalid
(that is in the wrong format), the reply message will be in the form “ERR<_>n<CR><LF>”, where “<_>” specifies a
space and “n” specifies an error number. Refer to Section 1.5 for the meanings of the error numbers.
The reply message for a command message is always in the form “ERR<_>n<CR><LF>”. If the command message was
valid, “n” (the error number) will be 0. If the message was invalid, “n” specifies an error number: refer to Section 1.5
for the meanings of the error numbers.
5.3 Query Messages
5.3.1 Introduction
The query messages that you send to the serial interface card are shown in Table 8; these are listed in alphabetical
message syntax order. The query messages are fully described in Section 5.3.2 to 5.3.13. A reply to a query message
can be in one of two formats; short reply or long reply. Use the format mode command message to select long or
short reply format (refer to Section 5.4.3).
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