Microprocessor Circuit; Sbep Serial Interface - Motorola GM328 Service Manual

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If the radio was switched off, the radio's µP will switch it on and vice versa. If the On/Off/Volume
knob is pressed while the radio is on, the software detects a low state on line ON OFF SENSE, the
radio is alerted via line ON OFF CONTROL and sends a data request message. The controlhead µP
will inform the radio about the pressed knob and the radio's µP will switch the radio off. If the radio is
switched on either manually or automatically it's +5V source switches on the controlhead's voltage
regulator U0861 via line 5 SOURCE and transistor Q0866 and the controlhead's microprocessor
starts execution.
4.4

Microprocessor Circuit

The controlhead uses the Motorola 68HC11K4 microprocessor (µP) (U0871) to control the LEDs
and the LCD and to communicate with the host radio. RAM and ROM are contained within the
microprocessor itself.
The microprocessor generates it's clock using the oscillator inside the microprocessor along with a 8
MHz ceramic resonator (U0873) and R0873.
The microprocessor's RAM is always powered to maintain parameters such as the last operating
mode. This is achieved by maintaining 5V at µP pin 76. Under normal conditions, when the radio is
off, USW 5V is formed by FLT A+ running to D0855. C0856 allows the battery voltage to be
disconnected for a couple of seconds without losing RAM parameters. Diode D0855 prevents radio
circuitry from discharging this capacitor.
There are 8 analogue to digital converter ports (A/D) on the µP. They are labeled within the device
block as PE0-PE7. These lines sense the voltage level ranging from 0 to 5V of the input line and
convert that level to a number ranging from 0 to 255 which can be read by the software to take
appropriate action.
Pin VRH is the high reference voltage for the A/D ports on the µP. If this voltage is lower than +5V
the A/D readings will be incorrect. Likewise pin VRL 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 microprocessor can determine the used keypad type by reading the level at port PE5.
Connections S0931 – S0935 are provided by the individual keypads.
The MODB / MODA input of the µP must be at a logic "1" for it to start executing correctly. The XIRQ
and the IRQ pins should also be at a logic "1".
4.5

SBEP Serial Interface

The host radio (master) communicates to the controlhead µP (slave) through its SBEP bus. This bus
uses only line BUS+ for data transfer. The line is bi-directional, meaning that either the radio or the
controlhead µP can drive the line. The microprocessor sends serial data via pin 79 and D0872 and it
reads serial data via pin 78. Whenever the microprocessor detects activity on the BUS+ line, it starts
communication.
When the host radio needs to communicate to the controlhead µP, it sends data via line BUS+. Any
transition on this line generates an interrupt and the µP starts communication. The host radio may
send data like display information, LED and back light status or it may request the controlhead ID or
the keypad ID.
Controlhead Model for GM398