Datasheet

8-MHz Crystal

Timer

Module

Diagnostics

Module

ADC

Oscillator

Divide-

by-2

CLKOUT

4 MHz

XIN XOUT

AFE4490

SBAS602F –DECEMBER 2012–REVISED OCTOBER 2013

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CLOCKING AND TIMING SIGNAL GENERATION

The crystal oscillator generates a master clock signal using an external 8-MHz crystal. A divide-by-2 block

converts the 8-MHz clock to 4 MHz, which is used by the AFE to operate the timer modules, ADC, and

diagnostics. The 4-MHz clock is buffered and output from the AFE in order to clock an external microcontroller.

The clocking functionality is shown in Figure 58.

Figure 58. AFE Clocking

TIMER MODULE

See Figure 59 for a timing diagram detailing the various timing edges that are programmable using the timer

module. The rising and falling edge positions of 11 signals can be controlled. The module uses a single 16-bit

counter (running off of the 4-MHz clock) to set the time-base.

All timing signals are set with reference to the pulse repetition period (PRP). Therefore, a dedicated compare

the 16-bit counter value is equal to the reference value in the PRF register, the counter is reset to '0'.

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