Backlights; Rotary And Push Button; Communication Interface; Accessory Connector - Motorola MTM800 User Manual

4.2 - 4

Backlights

The PWM output LCD_BL controls the current source Q201 and related circuitry. By this signal the
current through the backlight diodes on the display module is determined. The supply voltage for the
backlight diodes is the 23V source provided at J201 pin 32.
The PWM signal KPD_BL controls the brightness of the 3 colour LED. It is routed via Q324 to the
emitters of the two red/green switches Q404 and Q405. The digital signals LED_GREEN and
LED_RED enable the colour by applying a HIGH to the basis of the respective transis-
tor.Q504/Q505. When both switches are ON the light will be amber.
The digital signal KPD_BL_ON_OFF switches the keypad backlight ON or OFF by means of the
FET Q401.
The PWM signal LED_EMERG is low pass filtered by R414/C410 and controls the brightness of the
EMERGENCY key backlight.

Rotary and push button

The push button S401 connects the LOCK_ON signal to the FILT_A+. LOCK_ON is wired into the
keypad matrix. The rotary S401 produces pulses on the two outputs PULSE_A and PULSE_B of a
different phase when the knob is turned. These pulses are low passed R403 Expansion Head
Enhanced Enhanced - R404 and C405/C406.
The B output is then applied to the D inputs of the two D-Flip Flops U401 and U402. The signal
integrity of output A output is ensured by the two invert Schmitt triggers U403 and U404. The output
pulse of U403 is the clock input for D-Flip Flop U401 and latches the status of the B signal with the
rising edge. The second Schmitt trigger inverts the A signal another time and latches the B output
into the D-Flip Flop U402 with its rising edge. Furthermore it serves as an interrupt RSW_1 for the
OMAP, which is the required to read the outputs of the two D-Flop Flops RSW_2 and RSW_INT.
From the polarity of these two signals the OMAP can determine whether the rotary was turned
clockwise or counter clockwise. The Flip Flops get a reset from the general board-reset POR

Communication interface

In direct mount the radio and the Enhanced Control Head communicate with each other via a two
wire communication interface BUS+ and SCI_TX. This interface needs to be enabled by setting the
RADIO_COM_EN signal to LOW and the BUS_EN signal to HIGH.
RADIO_COM_EN enables the buffer U420-1 and supplies 5V to the operational amplifiers U421
and U422 via the transistors Q411 and Q412.
The BUS_EN signal connects the SCI_TX to the BUS+ line via Q410.
The speed of this interface is 115kBaud/sec.
The physical interface to the radio is J102 with the following signals: GROUND, ON_OFF CON-
TROL, FILT_A+, BUS+, HANDSET_AUDIO, 5VD and SCI_TX.

Accessory Connector

The accessory connector J101 complies to the GCAI standard and provides the following signals:
FRONT_ONE_WIRE, GPIO_3_PTT, HANDSET_AUDIO, USB_D-, GROUND, USB_VBUS,
INT_MIC, USB_D+, GPIO_4_HOOK and GPIO_0_PWR. For further information please refer to the
GCAI specification.
THEORY OF OPERATION (ENHANCED CONTROL HEADS)