Holtek HT827A0 Manual page 17

The chip reset status are shown below:
PC 0000H
Interrupt Disabled
Prescaler Cleared
Cleared. After a
WDT master reset, WDT
begins counting.
Timer/Event Counter Off
Input/Output Ports Input mode
Point to the top of
SP
the stack.
V
D D
R E S
Reset circuit
Audio output and volume control
The HT827A0 provides a current type D/A out-
put for driving external 8W speaker through an
external NPN transistor. The user must write
the voice data to the register DAL (20H) and
DAH (21H). Only 12 bits which include the high
nibble of DAL and the whole byte of DAH are
used. For the current type D/A output the high
nibble data of DAL must be written at first, and
then the DAH data is written.
There are 16 steps of volume controllable level
that are provided for the current type D/A out-
put. The user only writes the volume control
data to the VCR register (22H). Only the high
nibble of VCR are used. Note that writing 0H to
the high nibble of VCR doesn¢t denote mute out-
put. When bit 7 (SRON) of the TEMPO register
(29H) is set as ²1² the change of volume level is
valid. The following is a table of the 16 kinds of
volume level:
Code Volume
0000 xxxx 1/16
0001 xxxx 2/16
0010 xxxx 3/16
0011 xxxx 4/16
0100 xxxx 5/16
0101 xxxx 6/16
0110 xxxx 7/16
0111 xxxx 8/16
Volume level table
Note: ²xx² means don¢t care
17
HT827A0
Code Volume
1000 xxxx 9/16
1001 xxxx 10/16
1010 xxxx 11/16
1011 xxxx 12/16
1100 xxxx 13/16
1101 xxxx 14/16
1110 xxxx 15/16
1111 xxxx 16/16
March 15, 2000