µPD6121, 6122
7. ONE-SHOT/CONTINUOUS COMMAND TRANSMISSION MODE
7.1 One-shot Command Transmission Mode
In order to reduce the average transmission current, the µPD6120C, 6121G, and 6122G transmit data only
once, and thereafter transmit just the leader code and stop bit indicating that a key is depressed. As a result,
this transmission method (one-shot command transmission mode) has the following characteristics.
Advantages
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Average transmission current is reduced to 1/3 to 1/4 compared with continuous command transmission mode
Reduced software load for reception program (not all commands are processed all the time)
This mode distinguishes when a key is pressed several times successively and when a key is kept depressed.
Disadvantages
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If a command is not read the first time, it cannot be read a second time
If a signal transmission is interrupted while continuous commands are executed, subsequent commands cannot
be executed.
Moreover, when fOSC = 455 kHz, the average current to the infrared-emitting diode is roughly equivalent to
3 % of the peak current.
IAVE = (9 ms + 0.56 ms)/108 ms x 1/3 (duty) = 2.95 % (first command is ignored)
7.2 Continuous Command Transmission Mode
A continuous command transmission mode for transmitting data a second or more times is also available.
As shown in Figure 7-2, it is possible to continuously transmit commands for all the keys or for individual key
output lines simply by adding a diode D and connecting it to KI0 or KI/O.
In this case, the average transmission current is larger than that in the one-shot command transmission mode.
When fOSC = 455 kHz, the average current to the infrared-emitting diode is roughly equivalent to 9 % of the
peak current.
IAVE = (9 ms + 0.56 ms x 33)/108 ms x 1/3 (duty) = 8.48 %
Cautions 1. If the double input key (K21-K24) is used in the continuous command transmission mode,
double-input key transmission is not performed (D5 does not become 1).
2. When the voltage drop of the REM output is large, the signal is not transmitted accurately.
Therefore, keep the REM output current within 1 mA.
Figure 7-1 shows the continuous command transmission mode.
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NEC [ NEC ]
