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OVERVIEW: Digital Section
Zeus performs the following tasks:
• Assists RoadRunner in the control of the power-up and power-down sequence of the unit.
• USB communication with the factory Automated Test Equipment.
• Accesses to the external NAND flash memory and DDR memory.
• Communicates with the RF ICs (ROADRUNNER and SLEDGEHAMMER).
• Memory mappings and accesses Liquid Crystal Display.
• Monitors battery voltage, as well as RF power-amplifier and battery temperature.
• Modifies and stores user-selectable ergonomic preferences.
• Reads and writes iDEN radio-tuning parameters.
• Sends and receives commands with the base station through DSP.
• Re-channels the SLEDGEHAMMER synthesizer during hand off.
1.6.2 MCU Digital Phase Locked Loop (DPLL)
The MCU has a programmable, digital phase locked loop (DPLL) that uses the 16.8 MHz
clock as a reference. The MCU initially runs from the external reference at power up.
Software programs the MCU DPLL to 399 MHz and switches from the external reference
to the MCU DPLL after lock is reached
1.6.3 Host System Clock Synthesizer
There are two iDEN system clocks that are generated by Roadrunner and Sledgehammer.
The Roadrunner generates 32.768 kHz using the Roadrunner PLL, and the Sledgehammer
generates 33.6 MHz. The MCU Programmable Interrupt Timer (PIT) is run by the 32.768
kHz oscillator. The 33.6 MHz is divided by 2 in the Roadrunner to yield a 16.8 MHz signal,
which serves as reference frequency required by the MCU and DSP cores
1.6.4 Host System Clock Synthesizer
The power-on circuitry uses the ROADRUNNER /ON B-pin and the power On/Off button
to turn on the unit. When the On/Off button is pressed to turn on the unit, the ON pin is
shorted to ground, which turns on ROADRUNNER. The low-voltage detector provides the
initial, active low reset to the MCU. When the ROADRUNNER voltages become stable
(after a minimum of 450 ms), the ROADRUNNER delays the voltage coming up, and
supervisor IC that monitors the voltage on V2, recognizes this and holds off Reset. At this
point, the MCU sets the defaults for all the ICs. For instance, the SLEDGEHAMMER
default clock is set to 8.4 MHz (16.8 MHz divided by 2). The MCU must reprogram the
SLEDGEHAMMER to run off the 16.8 MHz frequency. In addition, the ZEUS boots off
of the High Clock, not the Low Clock (CKIL). At this point, the ZEUS begins running the
subscriber code. To turn off the unit, the On/Off button is pressed, causing the /ON B-pin
of the ROADRUNNER to short to ground. The ROADRUNNER which drives
ROADRUNNER SEL_INT on ZEUS and tells the MCU to turn off. The MCU turns off by
driving the STO (WDI input to ROADRUNNER) line low, which shuts down the voltage
regulators in the ROADRUNNER.
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6880401P59-O
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