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HE847701

HE80000 SERIES

March 26, 2004

Page 24 of 29

V1.03

This specification is subject to change without notice. Please contact sales person for the latest version before use.

0

DA Disable

The output current of the DAC is programmable by mask option MO_DACISEL:

MO_DACISEL[1:0] DAC output current

00

0.375 mA

01

0.75 mA

10

1.5 mA

11

3 mA

16. Pulse-Width Modulation

The pulse-width modulator (PWM) converts 7-bit unsigned speech data written to PWMC data register to

proportional duty cycle of PWM output. PWM module shares the PWMC data register with

Digit-to-Analog Converter. So PWM and DA output can exist at the same time. When PWM circuit is

enabled, it generates signal with duty ratio in proportion to the DA value.

DA = 0x20

DA = 0x80

DA = 0xE0

1 subframe

The PWM bit of VOC register controls register to enable the circuit and output driver. When PWM bit of

VOC is ‘0’, PWME bit and output drivers settings are both cleared. To use PWM for voice output, PWM

bit has to be set to ‘1’ first, then set PWME bit and enable output driver by setting the driver number. If

PWM bit is disabled and enabled again, the setting for driver and PWME bit will be clear.

The Fast Clock is gated through PWME bit of PWMC command register to provide the clock source of

PWM circuit when it is enabled. As PWM needs higher frequency to operate, it cannot generate correct

PWM signal in Slow clock only mode.

When the program enters into Sleep mode or Idle mode, it will automatically turn off all voice outputs by

clearing VOC[2..1] to ”00”. To activate voice output again when returning to Normal Mode, the VOC

register needs to be set again.

The PWM output volume can be adjusted by command register PWMC[6..4]. The bit 6 and 5 control 2

time driver, while bit 4 controls 1 time driver, thus it has 5 levels of driver output. By turning on/off the

internal drivers, the sound level of PWM output can be turned up and down. Please note that this

adjustment apply only to PWM, but not DA output.