Motorola pro7100 Manuel de service télécharger pdf (Page 52)

2-38 Theory of Operation

The µP determines the used keypad type and the control head ID by reading the levels at ports PC0

– PC7. Connections JU0852/3/4 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.

Voltage sense device U0832 provides a reset output that goes to 0 volts if the regulated 5 volts goes

below 4.5 volts. This is used to reset the controller to prevent improper operation.

2.11.4 SBEP Serial Interface

The host radio (master) communicates to the control head 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

control head µP can drive the line. The µP sends serial data via pin 50 and D0831 and it reads serial

data via pin 47. Whenever the µP detects activity on the BUS+ line, it starts communication.

When the host radio needs to communicate to the control head 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 control head ID or

the keypad ID.

When the control head µP wants to communicate to the host radio, the µP brings request line CH

REQUEST to a logic 0 via µP, pin 62. This switches on Q0823, which pulls line ON OFF CONTROL

high through diode D0821. A low to high transition on this line informs the radio, that the control head

requires service. The host radio then sends a data request message via BUS+ and the control head

µP replies with the data it wanted to send. This data can be information such as a key is pressed or

the volume knob rotated.

The control head µP monitors all messages sent via BUS+, but ignores any data communication

between host radio and CPS or Universal Tuner.

2.11.5 Keypad Keys

The control head keypad is a 6-key keypad (Model B) or a 10- key keypad (model C). All keys are

configured as two analog lines read by µP, pins 13 and 15. The voltage on the analog lines varies

between 0 volts and +5 volts depending on which key has been pressed. If no key is pressed, the

voltage at both lines is 5 volts. The key configuration can be thought of as a matrix, where the two

lines represent one row and one column. Each line is connected to a resistive divider powered by +5

volts. If a button is pressed, it will connect one specific resistor of each divider line to ground level

and thereby reduce the voltages on the analog lines The voltages of the lines are A/D converted

inside the µP (ports PE 0 - 1) and specify the pressed button. To determine which key is pressed, the

voltage of both lines must be considered.

An additional pair of analog lines and A/D µP ports (PE 3 – 2) is available to support a keypad

microphone, connected to the microphone connector J0811. Any microphone key press is processed

the same way as a key press on the control head.

2.11.6 Status LED and Back Light Circuit

All the indicator LED’s (red, yellow, green) are driven by current sources. To change the LED status

the host radio sends a data message via SBEP bus to the control head µP. The control head µP

determines the LED status from the received message and switches the LED’s on or off via port PB

7 – 0 and port PA4. The LED status is stored in the µP’s memory. The LED current is determined by

the resistor at the emitter of the respective current source transistor.

The back light for the LCD and the keypad is controlled by the host radio the same way as the

indicator LED’s using µP port PA 5. This port is a Pulse Width Modulator (PWM) output. The output

signal charges capacitor C0843 through R0847. By changing the pulse width under software control,

the dc voltage of C0843 and thereby, the brightness of the back light can be changed in four steps.

1 2 ... 47 48 49 50 51 52 53 54 55 56 57 ... 108 109

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Motorola pro7100 Manuel de service Page 52

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