Keypad; One Wire Interface; Gcai Gpios And Usb - Motorola MTM800 User Manual

THEORY OF OPERATION (ENHANCED CONTROL HEADS)
The internal display controller in the OMAP loads the images into the display.
The display module is connected to the main board by the 40 pin connector J201

Keypad

The keypad interface of the OMAP can read the keypad matrix (COL5 - COL0 / ROW4 - ROW0) and
discover which key has been pressed. The reading of the matrix is initiated by an interrupt.
The keypad PCB is connected to the main board by the 24 pin connector J401.

One Wire interface

The One Wire signal from the OMAP is connected via a level shifter Q305, D301 and R309/R310 to
a switch U301. The switch routes the One Wire interface either to the front GCAI connector or to the
rear of the remote back housing connector if present.
The direction of the switch is chosen by the OMAP GPO signal ONE_WIRE_SEL.

GCAI GPIOs and USB

The general purpose I/Os from the GCAI connector GPIO_0_PWR, GPIO_3_PTT and
GPIO_4_HOOK are shifted from a 3.3V level to the OMAP I/O level of 2.8V by the bi-directional
level shifters U302, U303 and U304. The direction of the signal is chosen by the OMAP GPOs
GPIO_0_DIR, GPIO_3_DIR and GPIO_4_DIR.
The general purpose I/Os from the GCAI GPIO_1 and GPIO_2 are also level shifted by U323 and
U325. As the USB signals D+ and D- share the same physical pin of the GCAI connector with the
two GPIOs GPIO_1 and GPIO_2, the two switches U321 and U322 route the respective signals
from the OMAP to the GCAI connector.
With the switches U326 and U327 the signals can be switched between the front GCAI connector
and the rear GCAI connector when a remote back head is present. The two switches are controlled
by the logical signal USB1_GPIO and USB_FRONT_REAR.
The digital signal USB_MODE_SEL switches the resistors R327 and R328 to GROUND when the
Enhanced Control Head USB is required to be host. If the Enhanced Control Head is an USB device
USB1_PUEN activates the pull up resistor R326.
When the Enhanced Control Head is USB host the signal USB_VBUS_ENA enables the power sup-
ply switch U324.
U324 provides 5V for USB to the FET switch and to the remote back head if present. The signal
VBUS_FET_EN activates the FET Q326, which then switches the 5V to the GCAI connector. U324
has an internal over current detection, which will switch OFF the 5V if too much current is drawn. At
the same time the signal VBUS_OC_DET goes to LOW and indicates the over current to the OMAP.
The comparator U328 compares the USB_VBUS signal with 3.3V and delivers a HIGH on
USB1_DET when the VBUS voltage exceeds 3.3V. If the Enhanced Control Head is USB master it
will detect its own voltage. When the Enhanced Control Head is USB device it will detect when a
master is applied.
4.2 - 3