TK-285/(N)
9
CIRCUIT DESCRIPTION
IC19
IC17
CPU
IC20
EEPROM
FLASH
6-2. Low battery warning
The battery voltage is monitored by the microprocessor
(IC19). When the battery voltage falls below the voltage set by
the Low Battery Warning adjustment, the red LED flashes to
notify the operator that it is time to replace the battery. If the
battery voltage falls even more (approx. 5.8V), a beep sounds
and transmission is stopped.
6. Control Circuit
The control circuit consists of microprocessor (IC19) and
its peripheral circuits. It controls the TX-RX unit and transfers
data to and from the display unit. IC19 mainly performs the
following;
1) Switching between transmission and reception by PTT
signal input.
2) Reading system, group, frequency, and program data
from the memory circuit.
3) Sending frequency program data to the PLL.
4) Controlling squelch on/off by the DC voltage from the
squelch circuit.
5) Controlling the audio mute circuit by decode data input.
6) Transmitting tone and encode data.
6-1. Memory circuit
Memory circuit consists of the CPU (IC19) and a flash
memory (IC17).
A flash memory has a capacity of 2M bits and contains the
transceiver control program for the CPU and the data for
operating features.
This program can be easily downloaded from an external
device.
●
Flash Memory
Note : The flash memory stores the data containing the FPU
(KPG-62D) program, Security Number (MPT Serial Number)
and firmware program (User mode, Test mode, Tuning mode,
etc.).
This data must be reinstalled when replacing the flash memory.
●
EEPROM
Note : The EEPROM stores tuning data (Deviation, Squelch,
etc.)
Realign the transceiver after replacing the EEPROM.
Low battery warning
The red LED flashes during
transmission
The red LED flashes and
continuous beep sounds
while PTT pressed
Battery condition
The battery voltage is low but
the transceiver is still usable.
The battery voltage is low and
the transceiver is not usable
to make calls.
6-3. Key input
If the clock is supplied to CLK terminal when the RES
terminal (CPU pin 78) of the decade counter (IC301) is set to
Low, Q0 to Q7 become High sequentially. Normally, KI1 and
KI2 are Low (pulled down). When any key is pressed. KI1 or
KI2 become High. The CPU detects which key is pressed,
according to the voltage of KI1 and Kl2 and clock timing.
Fig. 10
Key input
IC19
CPU
Q5
Q1
Q0
Q2
Q6
Q7
Q3
Vss
Vdd
RES
CLK
CL
CA
Q9
Q4
Q8
KI1
KI2
CK
KRST
IC301
16 keys
RESET
CLOCK
Q0
Q1
Q2
Q3
Q4
Q5
Q6
Q7
Q8
Q9
CLOCK
INHIBIT
CARRY
OUT
Fig. 11
Decade counter timing chart
Fig. 9 Memory circuit
