4-12 Technical Description 8525B/8528 Technical Service Manual
Issue 6 Publication No: 15-02036
4.5 Microprocessor Controller PCB (04-02451 and 04-
03031)
Circuits on the Microprocessor Controller PCB govern the functions of the
transceiver including the operator controls and displays. The microcontroller
on the board accepts inputs from within the transceiver and from the
operator’s controls. Under control of the program in the EPROM, it outputs
the data necessary to achieve the appropriate response to input signals.
The microcontroller is connected with other devices on the board by three
buses: a conventional microcontroller bus (8-bit data, 16 bit address) and
two ‘Inter-Integrated Circuit’ (I
2
C) buses.
Note that during the manufacturing period of the 8528 series transceiver the
microprocessor controller 04-02451 was replaced with that shown against
04-03031.
For reference, both sets of drawings have been included in this manual. The
following description relates to either microprocessor controller.
4.5.1 Microcontroller Bus
The microcontroller (IC11) is an 80C31 which is a member of the Intel 8051
8-bit microcontroller family. It has 128 bytes of internal RAM, no internal
program memory, two counter/timers, two external interrupt sources and an
internal clock oscillator.
The microcontroller 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 32 to 39 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 address latch enable (ALE) signal (IC11
pin 30) indicates to the latch when the address is present on the bus. The
high order address bits are provided directly on pins 21 to 28 of IC11.
The following external devices are connected to the bus:
• IC14—an EPROM containing radio control software and customer
channel information. The microcontroller selects the EPROM via the
program store enable (SE) signal (pin 29).
• IC10—a RAM device supplementing the microcontroller’s internal
RAM. It is selected via the Read or Write signals (IC11 pins 16 and 17)
in conjunction with address line 15 (IC11 pin 28).
• IC12—a triple tone generator used to generate all audio tones required
in the transceiver, e.g. emergency call tones, error beeps, etc. It is
selected via the Read and Write signals in the same way as IC10 but in
conjunction with address line 14 (IC11 pin 27).
Three audio tone outputs are generated within IC12 by dividing the clock
inputs on pins 18, 15 and 9 by factors programmed into its data input. The
clock input signal is derived from the microcontroller’s ALE output. During
those cycles when the microcontroller does not generate the ALE, the Read or
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