Voltage Regulator; Microcomputer; Interface Circuitry - Motorola ASTRO W3 Service Manual

Theory of Operation: W4, W5, and W7 Control Heads
Type
3 RECEIVE enabled by control head
ON/OFF switch; TRANSIT enabled
only when ignition switch is ON.
The ignition cable is the fused wire attached to the accessory connector. The control head is shipped
with jumper JU1 OUT and jumper JU2 IN. The three options are:
1. Connect the ignition cable to "Battery Hot" on the fuse block to TRANSMIT and RECEIVE via
the front panel pushbutton On/Off switch, regardless of the ignition setting.
OR
2. Connect the ignition cable to "Ignition" at the fuse block to disable TRANSMIT and RECEIVE
except when the ignition is on. This method is more convenient because you need only to
switch off your ignition; the radio will not drain your car's battery when you leave the radio
switch on.
3. To allow receive via front panel On/Offf, but inhibit transit when the ignition is off, control head
jumpers and radio software settings must be changed. Follow the disassembly procedures in
Chapter 5 to remove the control head PC board from its housing, and then locate JU1 and
JU2 using the board overlays in Chapter 8. Carefully unsolder JU2 from the board and solder
it in a JU1. Change the "ignition switch" field in CPS (Radio Wide/Advanced) or RSS (F4/F3/
F3/F3) to "TX inhibit."
For remote mounted radios, the same options of operation are available to the customer. The fused
GREEN wire coming from the control-head end of the interconnect cable is connected to "Battery
Hot." The ignition cable is the fused ORANGE wire also coming from the interconnect cable. The
control head is shipped with jumper JU1 OUT and JU2 IN. Configured this way, connections to the
ignition cable are made following options (1) or (2) above.
3.2.2

Voltage Regulator

Switch B+ is applied to U45, a 5-volt regulator. C45 and C58 filter SWB+ and the 5-volt line to ensure
U45 operated properly. CR90 protects against accidental reverse-polarity connections during
installation. The 5-volt supply operates the microcomputer circuitry, interface circuitry, vacuum
fluorescent (VF) driver U101, and comparator U3.
3.2.3

Microcomputer

The microcomputer, U1, operates on the 5-volt supply and is filtered by L1. A resonator, Y1,
oscillates at 4 MHz to provide a stable clock for microcomputer timing. U1 handles all communication
with the radio command board over the serial bus, scans the keyboard for button presses, and
generates the display information needed by the VF driver (U101) to drive the VF display (U102).
3.2.4

Interface Circuitry

The bulk of the interface circuitry is contained in bipolar, custom IC, U4. This IC includes watchdog
timer circuits, serial-bus communication drive circuits, and input buffer circuits to protect
microprocessor U1.
6881096C77-O
Table 3-2. Types of Operations (Continued)
How it Operates
Control Head
Jumper/Status
JU1 IN; JU2 OUT Connect ignition cable to
"ignition" at fuse block.
Enable "TX inhibit" ignition
switch setting in RSS or
CPS.
Ignition Wiring
September 26, 2003
3-5