User's Manual

For silent Alarm, any of the following will cause the mobile to exit Emergency:
o Extended keypress of the Emer button on the mobile's control head.
o Mobile mic PTT or a portable-to-base repeat.
2. The mobile will not unmute due to base traffic during silent alarm, and therefore
the priority VRS will not attempt a base-to-portable repeat. If there are other, non priority
VRS units in the area, they will perform the base-to-portable repeat without counting into
priority.
IMPORTANT NOTE: While in Emergency, attempts to send a
message or status from the portable will be ignored and WILL NOT cause the mobile to
exit Emergency.
6. Hardware Detailed
Theory of Operation
The VRS750 contains two main modules : an HT750 transceiver and an interface board.
I - The HT750 transceiver : This module is an Analog synthesized FM device that
contains the receiver, transmitter, and controller section (Refer to manual 68P81088C46-
A). A flex cable connects the HT750’s two accessory connectors to a single connector,
J30, on the interface board. The HT750’s RF jack is connected to W101 on the interface
board via the 50 ohm coaxial cable.
The VRS750 software is embedded in the HT750 digital portion of the controller which
consists of a microcontroller and associated EEPROM, RAM, and ROM memories.
II - The interface board: this board provide power regulation, bus translation circuitry,
audio routing circuitry, Single Tone Encoder and Decoder circuitry, programming
circuitry, and mode configuration.
Power Regulation:
The VRS750 is powered by the mobile’s Radio_SWB+ (13.8VDC) at the connector
P102-22. L101 and C137 are used to filter alternator whine from this signal before
providing it as SWB+ to the interface board. The VRS750 utilizes the mobile’s analog
(P102-2,11,21) and digital grounds (P102-18).
U111 regulates the SWB+ down to +5VDC. This voltage provides power for
several switching transistors and voltage dividers on the VRS750 board. U118 is a
micropower low dropout regulator used to provide +9.6V for all of the analog audio
circuitry. R162 and R164 form a divider network from this 9.6V to produce the 4.8V
(VAG) used to bias the audio circuits. Finally, U129 is a three-terminal regulator used to
provide the regulated 7.5V to the HT750 transceiver via Q113 in the reset circuit.
SW7.5V is provided to the HT750 at pad P31.
Bus Translation Circuitry:
The devices U100-2, U103, Q100, Q101, Q102, Q103, and Q104 are used to separate
messages from the bi-directional SB9600 serial bus Bus+, Bus-, and Busy into and from
the single direction RXD, TXD, BUSY OUT, and BUSY IN signals at the HT750.