Codan NGT 2010 RF Technical & Service Manual page 782

Signalling and microprocessor
Microcontroller bus
Drawing
The microprocessor IC12 on the Microprocessor & TCVR Interface PCB is an 80C552
and is a member of the Intel 80C51 8-bit microprocessor family. It has 256 bytes of
internal RAM, no internal program memory, two counter/timers, eight 8-bit ADC inputs,
a watchdog timer, I
The microprocessor operates in a conventional 8-bit data, 16-bit address configuration.
To minimise the pin count, the low-order address bits are multiplexed with the data on
pins 50 to 57 onto a common 8-bit bus. IC13 is used to latch the low-order address bits to
facilitate access to the external non-multiplexed devices. The ALE signal (IC12 pin 48)
indicates to the latch when the address is present on the bus. The high-order address bits
are provided directly on IC12 pins 39 to 46.
The following external devices are connected to the bus:
•
•
•
A voltage detector and reset generator IC9 resets the microprocessor if the 5 V supply
falls below 4.7 V.
Connected to the input ports of IC12 (pins 1, 66, 67, and 68) is a binary switch
(designated as Mode Select).
Temperature sensing is monitored by the microprocessor at ADC input pin 62, by
measuring the voltage at the resistor/thermistor circuit R36 and R37. Battery-voltage
sensing is measured at the resistor-divider network R38 and R39 and is connected to
ADC input pin 64.
2
Internal I C bus
Drawing
Additional to the address and data bus lines, the microprocessor has an I
connected to the backplane and is used to operate the following:
•
•
The I
NGT Transceiver System Technical Service Manual
04-02690
2
C bus, and an internal clock oscillator.
IC14—an EPROM containing control firmware. The microcontroller selects the
EPROM via the PSEN signal (pin 47).
IC15—a RAM device supplementing the microcontroller's internal RAM. It is
selected via the Read or Write signals (IC12 pins 30 and 31).
IC16—a triple-tone generator used to generate control tone and digital filter clocks
(see page 344, 300 Hz control tone—generation and
04-02541
IC2—DAC located on the Dual Line Equaliser PCB enables the microprocessor to
select 64 DC steps between 0 to 9 V to control the threshold, gain, and equalisation
amplifiers.
IC3—I/O 8-bit expander located on the Dual Line Equaliser PCB that has outputs to
control the transmit and receive audio paths.
2
C bus is also used to communicate to the General Purpose Input/Output PCB.
8571—Technical description
detection).
2
C bus that is
343