Power On / Off; Microprocessor Circuit - Motorola MTM800 User Manual

4.2 - 2
in U515 starts counting. When the output Q12 of U515 goes to HIGH, the output of the D-Flip Flop
U509 goes to HIGH and the OMAP is coming out of RESET.
In case the error output of U506 goes to LOW, the Flip Flop is cleared and thus the OMAP goes into
RESET. U515 is also held in RESET and the oscillator stops working.

Power On / Off

The Enhanced Control Head in dash mount configuration can be switched ON either by the ON
rotary push button, the ON button in the keypad, the EMERGENCY button or by the radio via the
accessory connector of the radio.
If one of the three buttons on the Enhanced Control Head is pressed, the OR circuitry D510, D511
produces the signal ON_OFF_CONTROL, that switches the radio ON. When the radio powers ON it
delivers a 5V level on the BUS+ and SCI_TX lines. The transistor couple Q508 then sets the signal
BUS_ON to HIGH and the regulator U501 is enabled.
When all regulators are powered and the RESET signal has gone to HIGH, the OMAP controller
starts operating.
The OMAP processor has to program the ON_HOLD line to HIGH in order to maintain the enable
signal for U501, when the BUS+ line is used for communication later on.
Before the first message can be transferred, the interface has to be activated 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 other possibility to switch ON is when the radio is switched ON from its accessory connector
either by IGNITION or by EMERGENCY. The regulator U501 is also enabled by the BUS+ signal in
this case.
The system can be switched OFF by either the ON/OFF button in the keypad or by the radio via the
IGNITION signal on the accessory connector.
If it is switched OFF by the ON / OFF button, the Enhanced Control Head communicates this to the
radio. After the radio has shut down the OMAP releases the ON_HOLD signal. If it is switched OFF
by the radio it is told by a message from the radio to switch OFF. It has then also to release
ON_HOLD.

Microprocessor Circuit

The Enhanced Control Head uses the TI microcontroller OMAP1621 (U201) to control the functions
of the Enhanced Control Head. The firmware is contained in a flash memory of 16Mbytes (U204).
When the firmware is executed it runs in the SRAM U205. Flash and RAM have a separate data,
address and control bus and operate at a 1.8V level.
The internal clock oscillator with the Xtal Y201 and the components R221 and C204/C205 generate
the system clock of 12MHz.
The 32.768 kHz clock mentioned above is also fed into the OMAP controller.
The power supply design assures that the core is powered first and then the I/O and USB voltages
are supplied to the controller. After this the system comes out of RESET.
THEORY OF OPERATION (ENHANCED CONTROL HEADS)