LM8322 datasheet(8/42 Pages) NSC

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9.0 Clocks

•

System Clock (mclk) — The system clock is in the range

of about 21 MHz (± 7%) typical. This clock is used to drive

the I2C compatible serial ACCESS bus and is the input

clock for other function blocks.

•

Processing and Command Execution Clock (t

C) — The

internal processing is based on a 2 MHz clock. This clock

is derived from the System Clock.

•

Internal PWM Clock — The internal PWM clock is a fixed

scaled down clock (÷ 64) of the Processing and Command

Execution Clock. This clock is close to 32 kHz which is in

a good range to source the PWM function block as an

alternative to an external clock source.

•

External 32.768 kHz Clock — driven into the SLOWCLK

input. May be used internally as the timebase for the PWM

and driven on the SLOWCLKOUT output.

•

External 32.768 kHz Crystal — connected across the

XTAL_IN and XTAL_OUT pins (XTAL_IN is an alternate

function of the SLOWCLK pin). May be used internally as

the timebase for the PWM and driven on the

SLOWCLKOUT output.

30013602

FIGURE 2. Clock Architecture

9.1 INTERNAL EXECUTION CYCLE

The Processing - and Command - execution clock is about 2

MHz. This clock is stopped in Halt mode, which only occurs

under control of the LM8322. However, the host can set the

period of inactivity which causes the device to enter Halt

mode.

Exit from Halt mode can be triggered by any of these events:

•

Occurrence of a key-press or key-release event.

•

A Start condition driven by the host on the ACCESS.bus

interface.

•

Assertion of the RESET input.

After reset, the default timebase for the PWM outputs is the

internal execution clock divided by 64.

9.2 BUFFERED CLOCK

The timebase for the PWM comes from any of three sources:

•

Prescaled internal Execution clock.

•

External 32.768 kHz clock received on the SLOWCLK

input.

•

On-chip oscillator with an external crystal connected

across XTAL_IN and XTAL_OUT.

Any of these sources may be buffered and driven on the

SLOWCLKOUT output. The clock buffer is enabled with the

WRITE_CLOCK command.

If XTAL_IN is not used it must be terminated to V

CC or GND.

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