Panasonic JB-3300 Technical Manual page 311

HARD RESET: Input Signal to Reset the Keyboard. Negative Logic
The keyboard is reset when HARD RESET is received from the system unit.
HARD RESET occurs at the timing shown in Figure 4-8, only after the number
5 +5 V terminal has reached 4.75 V or more.
+5 V
4.75 V
+5 V
l
GND ----- !
HARD
RESET
| 50 ms max |
m "
Figure 4-8 HARD RESET
Scanning
The circuit is a matrix composed of a scan driver and a scan detector (DBO
- DB7 of the microprocessor).
A low-active signal is output to the key matrix to detect which key is
depressed in the corresponding line. Signals are output directly from the
microprocessor to the driver. The output intervals differ slightly
depending on whether or not a key is pressed. Figure 4-9 shows an average
output interval.
Scale on the
abscissa: 1 ms/div
an oe
Top: Microprocessor
P24 output
NN Bottom: Microprocessor
P25 output
| |
Figure 4-9 Microprocessor Output to Scan Driver
Iv - 11