Keypad; Figure 4-5. Vhf Vco Block Diagram; Figure 4-6. Keypad Block Diagram - Motorola EP450 Service Manual

VHF Theory Of Operation: Keypad
C267, and varactor D262. High-port audio modulation from the synthesizer IC is applied as
VCO_MOD to varactor D261 which modulates the transmit VCO.
NC
NC
V_SF (U201 Pin 28)
Steer Line
Voltage
(V_STEER)
RX RX VCO
Tank Circuit
TX TX VCO
Tank Circuit
4.5

Keypad

The keypad block diagram is shown in
KEYPAD_ROW and KEYPAD_COL. These voltages are sent directly to the radio's microprocessor
on the main board. The microprocessor then interprets the voltage for KEYPAD_ROW and
KEYPAD_COL for each key press.
Keypad Row
Keypad
Button Keypad Column
HKLN4216A
TRB_IN
Pin 20
Pin 7
TX/RX/BS
Pin 13 Switching Network
Pin 3 Vcc-Superfilter
U251
VCOBIC
Collector/RF in
Pin 4
RX
Pin 5
Rx Active
Bias
Pin 6
Pin 16 TX
Tx Active
Bias
Pin 15
Vsens
Circuit
Pin 2
Pin 18
Rx-I adjust
Vcc-Logic
3V
(U330 Pin 5)

Figure 4-5. VHF VCO Block Diagram

Figure 4-6. Pressing a key creates two distinct voltages
Keypad Row
Keypad Column

Figure 4-6. Keypad Block Diagram

AUX3 (U201 Pin 2)
Pin 19
Prescaler Out
Pin 12
Presc
Buffer
Q280
Pin 8
RX
Pin 14
VCC Buffers
Pin 10
TX
Pin 1 Pins 9,11,17
Tx-I adjust
V_SF
(U201 Pin 28)
Keypad Row
Keypad Column
4-7
U201 Pin 32
RX INJ
3V (U330 Pin 5)
Matching
TX INJ
Network
MCP
November 24, 2003