Last updated: December 2, 2008
The frame trigger is a positive-going TTL compatible pulse that is one GSM bit wide, it is aligned to the downlink TDMA frame timing. The test set provides a frame trigger for synchronizing other test equipment to a measurement it is available at the rear-panel TRIG OUT connector.
The frame trigger has 3 parameters that the user must set. See CALL:TRIGger .
The External Trigger State parameter turns the external frame trigger on and off. See CALL:TRIGger[:OUTPut]:FRAMe:STATe for command information.
The External Trigger Timeslot parameter causes the external frame trigger pulses to align with the timeslot you specify. See CALL:TRIGger[:OUTPut]:FRAMe:TSLot for command information.
The External Trigger Symbol parameter causes the external frame trigger pulses to occur a user specified number of bits after bit 0 of the selected timeslot. See CALL:TRIGger[:OUTPut]:FRAMe:SYMBol for command information.
Each frame is made up of 8 time slots. Time slots are defined in "ETSI GSM 05.10 Ver. 4.9.0 Section 5. Time slots 0 and 4 are 157 bit periods long, time slots 1, 2, 3, 5, 6, 7 are 156 bit periods long, the average time slot is 156.25 bits in duration. The external trigger timeslot can be set to any time slot 0 through 7, the external trigger bit position can be set from 0 through 1250. If the trigger bit position is set to 1250, that is one full frame beyond the setting of the external trigger timeslot, (156.25 * 8 = 1250).
When the cell activated state is OFF, the frame trigger output is disabled (set to 0 volts) since there is no reference downlink TDMA frame structure available. However, the frame trigger state command ( CALL:TRIGger[:OUTPut]:FRAMe:STATe ) is not affected when there are changes to cell activated state.
The frame trigger can be set manually from the CALL SETUP screen by pressing the Cell Info softkey, then External Trigger Setup soft key.