Motorola pro7100 Manuel de service télécharger pdf (Page 48)

2-34 Theory of Operation

2.10 Control Head (PRO3100, CDM750)

ThE Control Head Contains the internal speaker, the on/off/volume knob, the microphone connector,

several buttons to operate the radio and several indicator Light Emitting Diodes (LED) to inform the

user about the radio status. To control the LED’s and to communicate with the host radio the control

head uses the Motorola 68HC11E9 µP.

2.10.1 Power Supplies

The power supply to the control head is taken from the host radio’s FLT A+ voltage via connector

J0801, pin 3 and the regulated +5V via connector J0801 pin 7. The voltage FLT A+ is at battery level

and is used for the LED’s, the back light and to power up the radio via on / off / volume knob. The

stabilized +5 volt is used for µP and the keypad buttons. The voltage USW 5V derived from the FLT

A+ voltage and stabilized by the series combination of R0822, VR0822 is used to buffer the internal

RAM of the µP (U0831). C0822 allows the battery voltage to be disconnected for a couple of

seconds without losing RAM parameters. Dual diode D0822 prevents radio circuits from discharging

this capacitor. When the supply voltage is applied to the radio, C0822 is charged via R0822 and

D0822. To avoid the µP entering the wrong mode if the radio is switched on while the voltage across

C0822 is still too low, the regulated 5 volt supply charges C0822 via diode D0822.

2.10.2 Power On/Off

The on/off/Volume knob, when pressed, switches the radio’s voltage regulators on by connecting line

ON OFF CONTROL to line UNSW 5V via D0821. Additionally, 5 volts at the base of digital transistor

Q0822 informs the control head’s µP about the pressed knob. The µP asserts pin 62 and line CH

REQUEST low to hold the line ON OFF CONTROL at 5 volts via Q0823 and D0821. The high line

ON OFF CONTROL also informs the host radio that the control head’s µP wants to send data via the

SBEP bus. When the radio returns a data request message, the µP informs the radio about the

pressed knob. If the radio is switched off, the radio’s µP switches 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

control head µP informs the radio about the pressed knob and the radio’s µP switches the radio off.

2.10.3 Microprocessor Circuit

The control head uses the Motorola 68HC11E9 microprocessor (µP) (U0831) to control the LED’s

and to communicate with the host radio. RAM and ROM are contained within the µP.

The µP generates it’s clock using the oscillator inside the µP along with a 8 MHz ceramic resonator

(U0833) and R0920.

The µP’s RAM is always powered to maintain parameters such as the last operating mode. This is

achieved by maintaining 5V at uP, pin 25. Under normal conditions, when the radio is off, USW 5V is

formed by FLT A+ running to D0822. Capacitor C0822 allows the battery voltage to be disconnected

for a couple of seconds without losing RAM parameters. Diode D0822 prevents radio circuits from

discharging this capacitor.

There are eight analog-to-digital converter ports (A/D) on the uP. They are labeled within the device

block as PE0-PE7. These lines sense the voltage level ranging from 0 to 5 volts 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.

The Pin VRH Pin is the high reference voltage for the A/D ports on the uP. If this voltage is lower than

+5V the A/D reading is incorrect. The VRL signal 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 could be incorrect.

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Motorola pro7100 Manuel de service Page 48

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