Motorola ASTRO XTS 5000 Detailed Service Manual page 56

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4.3.4.1.2 USB Transceiver
The USB transceiver, internal to the Flipper IC, is capable of transmitting and receiving serial data at
a rate of 12 megabits per second. The differential USB data comes from the side connector, through
the 22-ohm resistors R252 & R253 and the isolation switch Q301, and then to the USB_DPLUS and
USB_DMINUS pins on the Flipper IC. The USB receive interface from the Flipper IC to the Patriot IC
is as follows: USB_DPLUS routed to USB_VPI, USB_DMINUS routed to USB_VMI_RXD, and the
differential decoded data is output at the URXD_RTS pin and goes to the Patriot IC URTS1 pin.
The USB transmitter is enabled when the USB_SUSP and USB_TXENAB signals are both driven
low by the Patriot IC. The single-ended data is output from the Patriot IC on the UTXD1 pin and goes
to the Flipper TXD_USB_VPO pin. The data is driven out differentially on the USB_DPLUS and
USB_DMINUS pins, which go to the side connector. The Patriot IC sends the single-ended zero
signal from pin PC0_USB_VMOUT to the Flipper IC USB_FSEZ pin.
When a USB cable is detected, the USB_DIS pin (Q302 pin 2) goes high. This controls the isolation
switch Q301 so that the data that is on those lines are routed to the USB transceiver. If a USB cable
is not detected, the USB_DIS pin is low and the USB transceiver on the Flipper IC is isolated from
the side connector. This isolation is done primarily because the RS232 data lines are 5-volt lines, so
the switch protects the transceiver since it operates at 3 volts, and the USB data lines to the side
connector also act as the RS232 lines.
4.3.4.1.3 One-Wire Support
New options and accessories that attach to the side connector are identified by the Patriot IC using
the One-Wire protocol. The Option Select 2 pin on the side connector also serves as the One-Wire
data pin (R218). This signal is connected to the ONE_WIRE_OPT pin. This pin is connected to the
Patriot IC One-Wire bus ONE_WIRE_UP through an internal isolation switch controlled by a Patriot
IC GPIO line to the Flipper IC ONE_WIRE_EN_X pin. This isolation is needed to prevent possible
contention on the One-Wire bus when a smart battery is attached to the radio.
These new accessories are to ground pin 10, CTS (TP208), of the side connector. When this occurs,
the Flipper IC pin KVL_USB_DET_X is asserted and the Patriot IC detects the change. The Patriot
IC then asserts the ONE_WIRE_EN_X pin on the Flipper IC to connect the side connector One-Wire
line to the Patriot IC One-Wire bus. In the case of the USB cable, the Patriot IC reads the One-Wire
data from the cable and, upon determining that a USB cable is attached, programs the Flipper IC for
USB mode.
4.3.4.1.4 Watchdog Timer
The Flipper IC monitors the position of the radio's on/off button on the BP_SEN_X pin, and that
signal is located on Q508 pin 3. If the voltage on pin 3 is ground, then the radio is turned on. If the
voltage on pin 3 is 3 volts, then the radio is off. When the radio is turned off, a counter inside the
Flipper IC begins incrementing. That counter can be refreshed by the Patriot IC through the SPI bus.
This is done so that the software has enough time to complete its tasks before the power is taken
away from the Patriot IC. If the counter is not refreshed by the time the count is complete, the Flipper
IC pin WD_OUT goes low, which shuts down the GCAP II voltage regulators. During normal radio
operation, WD_OUT should be high (3 volts).
4.3.4.1.5 32 kHz Oscillator and CMOS output
The 32 kHz oscillator circuitry uses a separate voltage supply pin (VDD3_XTL) than the other 3-volt
portions of the Flipper IC. This 32 kHz clock is used by the GCAP II RTC module to keep track of
time. The VDD3_XTS pin is supplied with the backup lithium (Li) rechargeable battery voltage
LI_CELL. The oscillator circuitry is internal to the Flipper IC, and the 32.768 kHz crystal Y301 and
additional load capacitors C308 and C309 are located next to the IC.
April 15, 2002
Detailed Theory of Operation
: VOCON Board
68P81094C31-O