REV.-A
PRINCIPLES OF OPERATION
Power On or Off
D4, R40, and C19 in Figure 2-35 comprise an ON/OFF RESET circuit. The purpose of this circuit is to cause
the CPU to start from address 0000 hex. when power is applied and to prevent CPU malfunctions when
the power is switched off.
The rising edge of the Vx voltage cancels the RESET signal after a delay of time constant (R40 x C19),
which is produced by the integration circuit of resistor R40 and capacitor C19. The falling edge of the Vx
voltage activates a RESET signal by discharging capacitor C19 via diode D4.
The gate array (pins 49 to 51) is used for waveform shaping.
Vx Voltage
Pin 49 of IC7A
Reset output at
Pin 51 of IC7A
RESET
The CPU
RESET
I
I-
t
I-
*
Operates
Figure 2-36. RESET Output
LQ-510
2-29
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