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4.3
CIRCUIT DESCRIPTION
Power Supply
CN1 pin 4 is the unit circuit ground and the power supply ground.
CN1
pin 5 is the +5 V power supply which supplies +5 VDC +0.5% with a maximum
of 200 mA.
FG is connected to the keyboard metal chassis to protect it from electro-
Static charges.
|
Oscillator
6 MHz, the basic clock frequency cheated by the ceralock, is frequency-
divided into a fifteenth.
The resulting 400 kHz appears at pin 11 of the
microprocessor (Figure 4-16).
Scale on the
abscissa:
1 us/div
TL
|
Figure 4-1
ALE Waveform
This microprocessor operation can be checked by observing this waveform.
Data Type and Logic
G)
KBDATA:
Data output signal from the keyboard:
Positive logic
BUSY input signal from the system unit:
Negative logic
Oo
Data type
ON code:
Key data output when key is pressed.
OFF code:
Key data output when key is released.
The OFF code
is
(80) (HEX) plus the corresponding key data when the
key is pressed.
IV - 6
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