March 2003 M2303-00-P00-805 7
PTT Activated AVL Reporting
The A76 can be configured to send an unsolicited AVL report each time the PTT is pressed or released. Refer
to the PTT Activated AVL Reporting section.
FFSK Tone Blanking
Tone Blanking is used for applications in which voice and data share the same channel. When valid data is
received, the FFSK Tone Blanking mutes the radio. If the A76 detect either preamble or synchronisation bytes
in the received FFSK data, the speaker is muted using the squelch line. Refer to the Programming the A76
section for database configuration information.
Error Handling
‘old’ If the NMEA RMC data from the GPS receiver has the status flag set to ‘V’ (invalid),
the AVL report is marked as ‘old’.
‘not operational’ If no AVL data is received from the GPS receiver for 20 seconds, an AVL report
marked ‘not operational’ is sent. The will occur if the GPS receiver is disconnected.
‘format error’ If a data error occurs, an AVL report is marked ‘format error’ is sent. This may be
due to mismatched baud rates, an incorrect checksum or corrupt NMEA data.
Refer to section 8, Responses from the Remote Radio, for the response message format details.
A76 Configuration
Programming using NMEA
The serial RS232 serial port on the A76 modem is configured to expect NMEA type format. This means that
the programming of the A76 database must be done using NMEA sentences rather than sending a standard
CCDI Program command as is used with both the T2000-A75 Modem and the Tat Orca/Tait Radio Modem.
For this purpose four new Tait proprietry NMEA messages have been created:
• PTPGM - for programming the database configuration
• PTWDB - response from the A76 ro a PTPGM message
• PTRDB - for reading the database configuration
• PTDAT - response from the A76 ro a PTRDB message
Refer to the Programming the A76 section for details of the PTPGM settings.
Remote programming of Group Delay Time
The Group Delay Time is the only database configuration item that can be programmed remotely.
This is done using the Program Database command with a SEND_SDM CCDI message. Refer tothe Commands
to the Remote Radio section for further details.
The Group Delay Time determines the time that a radio waits before responding to a AVL report Poll. This is so
that when a Group Poll is sent, all the radios in the group respond at different intervals rather then
simultaneously.
