HT49CA1 View Datasheet(PDF) - Holtek Semiconductor
Part Name
Description
MFG CO.
'HT49CA1' PDF : 58 Pages View PDF
HT49RA1/HT49CA1
Carrier Generator
Some remote control transmitter applications require a
carrier frequency generator to transmit the remote con-
trol signal at the appropriate frequency to the receiving
device. These devices include an internal carrier fre-
quency generator for this purpose, the frequency of
which is specified by selecting the correct configuration
options.
This carrier signal is supplied on the REM pin, which is
also pin-shared with PC0. The selection of the required
function, whether remote output or CMOS output, is im-
plemented by selecting the required configuration op-
tion. If the remote output REM is selected by
configuration option, the REM output will be activated if
the PC0 data bit in the PC register is set to high. This
output data bit is used as the on/off control bit for the
REM output. Note that the REM output will be low if the
PC0 output data bit is set to zero. However, if the line is
configured as a PC0 output pin it will switch to a high
level and remain so until the application program resets
the pin to a zero. It is therefore important to note that, for
OTP devices, if the pin is configured as a PC0 output
pin, and a NPN transistor is connected to this output to
drive an infrared LED, the LED will be turned on during
this power-on reset period. For general purpose remote
controller applications, it is therefore recommended that
the REM configuration option is selected together with
an external NPN transistor to drive the infrared LED.
The clock source for the Carrier Generator is supplied
by the system clock divided by 4. By selecting values for
²m² and ²n² using configuration options in association
with the following equation the required carrier
frequency can be generated.
Clock Source
Carrier Frequency =
mx2n
The value of ²m² can be either 2 or 3 while the value of
²n² can range from 0 to 3, both values are chosen by se-
lecting the required configuration options. If ²m² is equal
to ²2² the duty cycle of the output waveform will always
be equal to 1/2. If ²m² is equal to ²3², with the exception
of ²n² being equal to ²0², the duty cycle can be either 1/2
or 1/3, the actual value of which is determined by config-
uration options.
m´2n
Duty Cycle
2, 4, 8, 16
1/2
3
1/3
6, 12, 24
1/2 or 1/3
The following table shows examples of different carrier
frequencies:
fSYS
fCARRIER
Duty
m´2n
37.92kHz 1/3 only
3
455kHz
56.9kHz 1/2 only
2
F r e q u e n c y D iv id e r
fS Y S /4
3 - b it C o u n te r
C o n fig u r a tio n O p tio n
C a r r ie r D u ty
1 /2 o r 1 /3
C o n fig . O p tio n
S e le c t
C o n fig u r a tio n
O p tio n
S e le c t
P C 0 D a ta R e g is te r
Carrier Signal Generation
R E M /P C 0
Rev. 1.10
29
March 30, 2014
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