PD17225_15 Datasheet, PDF (35/86 Pages) Renesas Technology Corp – 4-BIT SINGLE-CHIP MICROCONTROLLER FOR SMALL GENERAL-PURPOSE INFRARED REMOTE CONTROL TRANSMITTER

µPD17225, 17226, 17227, 17228
5.3 Carrier Generator Circuit for Remote Controller
µPD17225 is provided with a carrier generator circuit for the remote controller.
The remote controller carrier generator circuit consists of a 7-bit counter, NRZ high-level timer modulo register
(NRZHTMM), and NRZ low-level timer modulo register (NRZLTMM). The high-level and low-level periods are set in the
corresponding modulo registers through the DBF to determine the carrier duty factor and carrier frequency.
The system clock (fX) is divided by two and is input to the 7-bit counter. Therefore, when a 4-MHz resonator is used,
2 MHz (0.5 µs) is input to the counter as the clock; when a 32-kHz oscillator (fXT) is used, 16 kHz is input.
The NRZ high-level output timer modulo register is called NRZHTMM, and the NRZ low-level timer modulo register
is called NRZLTMM. Data is written to these registers by the PUT instruction. The contents for these register are read
by the GET instruction.
Bit 7 of NRZLTMM specifies whether the carrier or high level is output to the REM pin. To output the carrier, be sure
to clear bit 7 to 0.
5.3.1 Remote controller signal output control
The REM pin, which outputs the carrier, is controlled by bits NRZ and NRZBF for the register file and timer 0. While
the NRZ content is “1”, the clock generated by the remote controller carrier generator circuit is output to the REM pin; while
the NRZ content is “0”, the REM pin outputs a low level. The NRZBF content is automatically transferred to NRZ by the
interrupt signal generated by timer 0. If data is set in NRZBF in advance, the REM pin status changes in synchronization
with the timer 0 counting operation.
If the interrupt signal is generated from timer 0 with the REM pin at the high level, NRZ being “1”, and the carrier clock
at the high level, the REM pin output is not in accordance with the updated content of NRZ, until the carrier clock goes
low. This processing is useful for holding the high level pulse width from the output carrier constant (refer to the figure
below).
When the content of NRZ is “0”, the remote controller carrier generator circuit stops. However, if the clock for timer
0 is output from the remote controller carrier generator circuit, the clock continues to operate, even when the NRZ content
becomes “0”.
An actual example showing a remote controller signal output to the REM pin is presented below.
Data Sheet U12643EJ2V0DS00
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