Enhanced Control Head In Remote Mount Configuration; Remote Mount Back Head - Motorola MTM800 User Manual

THEORY OF OPERATION (ENHANCED CONTROL HEADS)

Enhanced Control Head in Remote Mount configuration

In remote configuration a remote mount back housing is attached to the back of the Enhanced Con-
trol Head.
It is connected to the Enhanced Control Head main board through J603.
A 10 pin Remote Mount cable on P101 connects the Remote Mount Back Housing Board to the
radio transceiver with either Expansion Head Enhanced or remote head.
A 25 pin connector J105 gives access to the GCAI GPIOs, second USB, 4-wire RS232, Rear GCAI
Pins and Audio.
The remote mount back head is detected by the OMAP by sending an I2C Bus request by means of
the I2C clock and data lines I2C_SCL and I2C_SDA.
The routing of the GCAI GPIOs and the first USB is described already in the dash mount chapter.
The 4-wire RS232 is connected to the UART 3 of the OMAP microcontroller. The signals for realiz-
ing the second USB port are directly provided by the OMAP and connected through the 40 pin con-
nector J601 to the remote mount back housing board. The ON_OFF_CONTROL, BUS+, SCI_TX as
well as the HANDSET_AUDIO and MIC lines are also routed via J602 to the rear of the remote
mount back head.
The remote mount back head itself is controlled by I2C messages and the remote mount back head
creates an interrupt to the OMAP when it has an I2C Bus message to deliver.
When the device was switched ON from the rear IGNITION line, the signal RM_ON turns to HIGH
and switches the signal GCAI to HIGH by means of D350 and Q353. Then the same ON procedure
starts as in dash mount configuration. After the device is in ON_HOLD and the OMAP has detected
the ON source on the remote mount back housing it sent a LOW on RM_GCAI_PWR_ON_CLR to
clear the RM_ON.

Remote Mount Back Head

Power supply
The remote mount back head is supplied from the Enhanced Control Head main board with the
FILT_A+ and unswitched 5 V when the device is switched OFF. When the device is switched ON by
either the Enhanced Control Head front panel or from the radio accessory connector, VCC_2.8V,
VCC_3.3V and the switched 5V will be also provided by the Enhanced Control Head main board.
When the device is switched ON from the rear IGNITION on the 25 pin rear connector by pulling
J105 pin 25, to the battery voltage, the Transistor Q401 provides a rising edge to the D-Flip Flop
U401 clock input. This latches the HIGH level on the D-input of U401 and creates an HIGH on
RM_ON. This turns ON the Enhanced Control Head main board as described above. At the same
time a HIGH on IGN_SENSE is applied to the I2C port expander U501 and generates an interrupt to
the OMAP. When the main board has powered ON as described above it clears the Flip Flop by pull-
ing RM_GCAI_PWR_ON_CLR to LOW.
An optional 5V can be turned ON supplying the rear GCAI (U304) even when NGCH is turned OFF.
RS232
The MAX3232E U303 transceiver provides level translation to RS232 levels of the 4 wire RS232
interface connected to UART3 of the OMAP that is internally routed to the camera interface.
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