HT47C20L View Datasheet(PDF) - Holtek Semiconductor
Part Name
Description
MFG CO.
'HT47C20L' PDF : 55 Pages View PDF
HT47C20L
Voltage Low Detector
The HT47C20L provides a voltage low detector for bat-
tery system application. If the battery voltage is lower
than the specified value, the battery low flag (BLF; bit 5
of RTCC) is set. The specified value is 1.2V±0.1V. The
voltage low detector circuit can be turn On or Off by writ-
ing a ²1² or a ²0² to BON (bit 3 of RTCC register). A de-
lay time of 1ms is required to monitor the BLF after
setting the BON bit. The BLF is invalid when the BON is
cleared as ²0². The voltage low detector can be disabled
by mask option.
Buzzer
HT47C20L provides a pair of buzzer output BZ and BZ,
which share pins with PA0 and PA1 respectively, deter-
mined by mask option. Its output frequency can also be
selected by mask option.
When the buzzer function is selected, setting PA.0 and
PA.1 ²0² simultaneously will enable the buzzer output
and setting PA.0 ²1² will disable the buzzer output and
setting PA.0 ²0² and PA.1 ²1² will only enable the BZ
output and disable the BZ output.
PA1
0
(CLR PA.1)
1
(SET PA.1)
X
PA0
0
(CLR PA.0)
0
(CLR PA.0)
1
(SET PA.0)
Function
PA0= BZ
PA1= BZ
PA0= BZ
PA1= 0
PA0= 0
PA1= 0
Buzzer Enable
Programmable Frequency Divider - PFD
The PFD output shares pin with PA3 as determined by
mask option.
When the PFD option is selected, setting PA3 ²0² will
enable the PFD output and setting PA3 ²1² will disable
the PFD output and PA3 output at low level.
PA3
Function
0 (CLR PA.3)
PA3= PFD Output
1 (SET PA.3)
PA3= 0
PFD output frequency=
1´
1
2 timer overflow period
Low Voltage Reset - LVR
The low voltage reset circuit is used to monitor the power
supply of the device. If the power supply voltage of the de-
vice is lower than 1.1V±0.1V, the device will automatically
reset internally. It is enabled or disabled by mask option.
The LVR includes the following specification:
· The low voltage (lower than 1.1V±0.1V) must be main-
tained for over 1ms. If the low voltage state does not ex-
ceed 1ms, the LVR will ignore it and does not perform
the reset function.
· The LVR uses the ²OR² function with the external
RES signal to perform chip reset.
· During HALT mode, if the LVR occurs, the device will
wake-up and the PDF flag will be set as ²1², the same
as the RES reset.
Bit No.
0
1
2
3
4
5
6, 7
Label
RT0
RT1
RT2
BON
¾
BLF
¾
Read/Write
R/W
R/W
¾
R
¾
Reset
1
1
1
0
¾
X
¾
Function
8 to 1 multiplexer control inputs to select the real time clock
prescaler output
Voltage low detector enable/disable control bit
²0² indicates voltage detector is disabled
²1² indicates voltage detector is enabled
Unused bit, read as ²unknown²
Battery low flag
²0² indicates that the voltage is not low
²1² indicates that the voltage is low
Unused bit, read as ²0²
Note: ²X² means ²invalid²
RTCC (09H) Register
Rev. 2.30
26
December 2, 2005
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