– 6 –
Key Scan
The Key Scan circuit uses an analog circuit to generate and send voltage to
the CPU when a key is pressed. The CPU uses this voltage to determine
which key was pressed. This resistive circuit eliminates the need for
encoder/decoder devices, simplifying design and adding to the reliability of
the receiver.
The CPU performs a key scan approximately every 20ms to check for a
pressed key. When the key data change is the same for two consecutive
reads, it is determined that a key has been pressed and the corresponding
command executed.
The table below shows the voltages input to CPU pin 9 when a given key is
pressed.
Key Input
The function of the keys on keyboard and those of the remote control
transmitter are the same.
The following keys, when activated, perform a series step action. The time of
each series step action is also shown below.
A . CH Up/Down 500 ms/step.
B . Vol Up/Down 140ms/step. It takes about 9 seconds to change from
minimum to maximum volume.
Preceding and succeeding mutes are performed when turning power Off/On,
changing channels, switching Antenna mode, searching channels, changing
MTS or TV/AV mode, exchanging programs between the main screen and
PIP window, or switching Surround sound mode.
Channel and Mode Change Mutes
MUTE SIGNAL
MUTE OFF
MUTE ON
PRECEDING
MUTE
SUCCEEDING
MUTE
MODE CHANGE
PRESSING KEY
MODE OUTPUT
Key Scan Voltages
KEY
INPUT VOLTAGE
FUNCTION
SW1901
4.26 ~ 5.00
POWER
SW1902
3.63 ~ 4.26
VOL +
SW1903
3.01 ~ 3.63
VOL -
SW1904
2.38 ~ 3.01
CH
▲
SW1905
1.60 ~ 2.38
CH
▼
SW1906
1.13 ~ 1.60
MENU
OFF
0.00 ~ 1.13
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KEY SCAN CIRCUIT
