UPD17217GT datasheet(32/84 Pages) NEC

32 / 84 page

µPD17215, 17216, 17217, 17218

5.3

Carrier Generator Circuit for Remote Controller

µPD17215 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 period setting modulo register

(NRZHTMM), and NRZ low-level period setting 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 oscillator 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 period setting modulo register is called NRZHTMM, and the NRZ low-level period setting

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.

When bit 7 of NRZLTMM is 0 (carrier output)

NRZ

REM

MAX. 500 ns (delay)*

(f = 4 MHz)

REM pin does not go low

until carrier goes low

even if NRZ becomes 0

*: Value when (TMCK1, TMCK0)

≠ (1, 1).

When (TMCK1, TMCK0) = (1, 1), the value differs depending on how NRZ is manipulated. If NRZ is set by an

instruction, the width of the first high-level pulse may be shortened. If NRZ is set by data transferred from NRZBF,

the high-level pulse is delayed by the low-level pulse of the carrier clock.

UPD17217GT Datasheet(PDF) 32 Page - NEC

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