Control Head Model A2 Or A3 - Motorola GM950E Service Manual

Controller
C0622 allows the battery voltage to be disconnected for a couple of seconds without losing RAM
parameters. Diode D0621 prevents radio circuitry from discharging this capacitor.
U0101-22 is the high reference voltage for the A/D ports on the E9/20µP. Resistor R0105 and
capacitor C0105 filter the +5V reference. If this voltage is lower than +5V the A/D readings will be
incorrect. Likewise U0101-21 is the low reference for the A/D ports. This line is normally tied to
ground. If this line is not connected to ground, the A/D readings will be incorrect.
The MODB (U0101-25) input of the E9/20µP must be at a logic 1 for it to start executing correctly.
The XIRQ (U0101-45) and the IRQ (U0101-46) pins should also be at a logic 1.
Optional external EEPROM (U0108) is available on some radio models. The external EEPROM is
accessed through a serial connection. The E9/20µP generates SPI CLK (U0101-53), SPI
TRANSMIT DATA (MOSI) (U0101-52) and SPI RECEIVE DATA (MISO) (U0101-51) to read or write
EEPROM. On a read of EEPROM the E9/20µP continues generating the clock and the EEPROM
places the requested data on the SPI RECEIVE DATA (MISO) line. On a write the message is
followed by the data to be written to the EEPROM.
2.12

Control Head Model A2 or A3

Two Control Head versions (A2 or A3) are available for user interface. Both Control Heads contain
the internal speaker, the microphone connector, several buttons to operate the radio and several
indicator LEDs to inform the user about the radio status. Additionally the Control Head model A3
uses a 3 digit, 7 segment, LCD display for the channel number.
The On/Off button when pressed switches the voltage regulators on by pulling ON OFF CONTROL
to high and connects the base of Q0925(A3), Q0825(A2) to FLT A+. This transistor pulls the line
ANALOG 3 to low to inform the µP that the On/Off button is pressed. If the radio is switched off, the
µP will switch it on and vice versa. All other buttons work the same way. If a button is pressed, it will
connect one of the 3 lines ANALOG 1,2,3 to a resistive voltage divider connected to +5V. The
voltages of the lines are A/D converted inside the µP and specify the pressed button.
All the back light and indicator LEDs are driven by current sources and controlled by the µP via
SERIAL PERIPHERAL INTERFACE (SPI) interface. The LED status is stored in shiftregister
U0941(A3), U0841(A2). Line LED CE enables the serial write process via Q0941(A3), Q0841(A2)
while line LED CLCK BUF shifts the data of line SPI DATA BUF into the shiftregister.
In addition Control Head Model A3 contains the LCD display H0931. The display data of line SPI
DATA BUF is shifted into the display driver by clock signal LCD CLCK BUF.
6.3-6 Theory of Operation