Safeline Signature Operating And Instruction Manual page 135

All data is represented as ASCII characters.
Application layer specification (OSI layer 7
The application layer operation can be split into various types of messages :-
1. Event driven messages.
These messages are prompted by an event occuring inside the detector. These events can be one of
the following list and are given in their order of priority when passed to the data-link layer for
transmission :-
a) Faults, extended faults (see command identifiers 'e' & 'F').
b) Signal Transmissions, ('A'n and 'R'n when enabled by 'g'0 command).
c) Logins using a security code at the keypad / Logout via PROG/EXIT key (or time out).
d) Reserved for future development.
e) Detector settings altered at the keyboard by an operator.
f) Detector settings altered by a communications command.
2. Host commands.
These are messages, initiated by the host, to change the settings of the detector or to read the settings of the
detector.
3. Detector responses to host commands.
4. These messages are responses to host commands, and are sent by the detector.
If, in the unlikely case of the serial output buffers being filled, higher priority messages will be transmitted at the
expense of lower priory messages.
Test Mode
For the purpose of checking the serial link, the detector will double echo any character sent as long as the serial link
is idling. The following character should not be sent, as they are recognised as part of a normal communication
transmission:- STX, ACK, NAK.
Priority of Host-Computer Vs Detector
The Host Computer or Intelligent equipment always takes priority over the detector when changing detector settings.
If the user is logged into the detector via its control panel and the Host Computer or Intelligent equipment changes
one of the detectors settings, the detector will be forced to log off and return to its running mode display.
4618 - 021
)
APPENDIX D
119