Motorola pro7100 Manuel de service télécharger pdf (Page 49)

Theory of Operation 2-35

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 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.

2.10.4 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 uP, 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 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 uP brings the 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

uP replies with the data it wanted to send. This data can be information like which key has been

pressed or that the volume knob has been rotated.

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

between the host radio and CPS or universal tuner.

2.10.5 Keypad Keys

The control head keypad is a 6-key design. 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) are 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 a control head.

2.10.6 Status LED and Back Light Circuit

All 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 keypad is controlled by the host radio the same way as the indicator LED’s

using uP port PA 5. The µP can switch the back light on and off under software control. The keypad

back light current is drawn from the FLT A+ source and controlled by 2 current sources. The LED

current is determined by the resistor at the emitter of the respective current source transistor.

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Motorola pro7100 Manuel de service Page 49

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