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Circuit Description
8
Transmit
Serial transmit Data is fed into the Magic IC. On the rising edge of DMCS, Magic
IC samples a TX data bit from the SDTX line. An additional TX data bit is sampled
from the SDTX line on every bit clock interval until DMCS goes low. A gated bit
clock is provided at TX_CLK. This clock is inverted from the internal bit clock. Thus,
when TX_CLK transitions from low to high, a new SDTX bit is sent. The Magic IC
reads SDTX on the high to low transition of TX_CLK.
Magic IC contains a look-up ROM to trace out frequency versus time corresponding
to GMSK modulation. The modulator will use the present data bit and the previous
three data bits to set up one of 16 possible waveforms based on the sum of Gaussian
pulses stored in a look up ROM. The resulting signal will then be clocked out at a
16X oversample rate. This data pattern will be input to a four-accumulator frac-
tional N synthesizer with 24-bit resolution.
The charge pump signal is an error voltage supplied from the phase detector
internal to the Magic IC. It is an error voltage and is used to tune the TX VCO to
the transmit frequency. It first passes through the Tx loop Filter. The circuit is
designed to charge a capacitor when TX_EN is initiated to hold the value for the
TX VCO during the burst. Data appears on the TX_CP at the same time DM_CS
occurs. The circuit, is basically a sample and hold circuit, which takes a sample of
the charge pump amplitude voltages and adjusts the charge pump voltage. This
corrected voltage is used to tune the TX VCO to the transmit frequency.
Controller
During power-up, the controller checks for battery presence and measures its
temperature and voltage. Charger presence and type are also sensed, the keypad
and display backlights are turned on, and the 13 MHz clock is started.
The SIM (subscriber identity module) interface is part of the Whitecap IC and
supports both synchronous (prepay card) and asynchronous serial data transmis-
sion, as well as both 3V and 5V cards.
The charger is capable of supplying the 400mA of current required to support the
Personal Communicator in standby while, at the same time, charging its internal
battery. Charging current is monitored by the GCAP II. In transmit, the Personal
Communicator requires up to 1.5A to be supplied during each burst. During a TX
pulse the full 400mA from the charger supports B+ in addition to approximately
1.1A from the battery.
Deep sleep mode saves battery life by intermittently shutting off part of the PCB.
Deep sleep mode shutdown is only for a fraction of a second and, during that time,
the GCAP Clock supports the logic side of the unit. This clock, output from GCAP
and fed directly to Whitecap IC, is monitored by Whitecap IC and, should it fail, the
unit is prevented from going into deep sleep mode.
The keypad interface consists of five row and five column pins. The rows are inputs
and the columns can be configured either as inputs or outputs. When operating with
columns as inputs, any active row or column signal will result in an interrupt. The
front keys on the PCB use a three contact design, one of which is tied to ground,
while the other two are pulled high and connected to the row and column inputs.
When a key is pressed all three of its pads are shorted and grounded. Since each
key is uniquely distinguished by the two lines pulled low, no strobing of the keypad
is necessary.
The display is a [64 X 126] pixel graphics display and is connected to the PCB via
a heat seal connector. The antenna PCB is connected to the controller via a flex
MOTOROLA CONFIDENTIAL - PROPRIETARY
November 20, 2000
Product Family 38C
6881036B20
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Troubleshooting
