Section 5
Page 5 - 32
HA243821
Issue 5 Mar 98
MODEL 346 INSTALLATION AND OPERATION MANUAL
5.7.4 PROTOCOL (Cont.)
POLLING SEQUENCE (CONT.)
ENQ
Enquiry. The polling message is terminated by the ENQ control character.
Table 5.7.4b Group and Unit IDs 10 to 15
POLL RESPONSE
In response to the poll message, the recorder will respond with either a poll completed message or a poll incom-
plete message. If however, the address sent is not recognised, the recorder will not respond at all.
POLL COMPLETED
A successful poll will result in the recorder returning the required data held within a message of the following type:
STX CN C1 C2 D1 to DN ETX BCC where CN, C1 and C2 are as described above, and the other mnemonics
are as follows:-
STX
Start of Text. This immediately precedes the text to be sent to the host
D1 to DN Data bytes. The N data bytes containing the parameter value requested. The number of characters
sent depends on the format of the particular parameter. These formats are detailed later in this docu-
ment.
ETX
End of Text. This character terminates the data transmission and alerts the host to the fact that the next
character to arrive will be the block check control (BCC) byte.
BCC
Block Check Control. This is a form of data checking, to ensure that no errors have occurred in the
transmission of the message. BCC is calculated by exclusive ORing the hex values of CN with C1,
then the result of this with C2, the result of this with D1, and so on up to and including ETX. The final
XORing produces BCC. For details see the example below.
POLL INCOMPLETE
If the recorder recognises the group and unit addresses, but some other part of the message cannot be deci-
phered, it will respond with a message of the type: STX CN C1 C2 EOT. The host must then initiate a complete
new polling sequence before it can receive any more parameter data.
10
11
12
13
14
15
:
;
<
=
>
?
Address
Character
