MV20556 Datasheet, PDF (18/30 Pages) Mosel Vitelic, Corp – 8 - Bit MCU Mouse Controller

MOSEL VITELIC INC.
Preliminary
External Interface (Cont'd)
processor via #INT0 or #INT1. This power-failure signal
must be early enough to allow the MV20556 before VDD
falls below its operating limit. The program servicing the
power-failure interrupt request must save any important
data and machine status into Internal Data RAM. The
service program must also enable the backup power
supply to the RES pin. Applying power to the RES pin
resets the MV20556 and retains the internal RAM data
valid as the VDD power supply falls below limit. Normal
operation resumes when RES is returned low. Figure on
last page left column shows the waveforms for the
power-down sequence.
Timing Generation
Timing generation for the MV20556 completely self-
contained, except for the frequency reference which can
be a crystal or external clock source. The on-board
oscillator is a parallel anti-resonant circuit with a frequency
range of 3 M to 40 MHz. The XTAL2 pin is the output of a
high-gain amplifier, while XTAL1 is its input. A crystal
connedted between XTAL1 and XTAL2 provides the
feedback and phase shift required for oscillation. The 3 to
40 MHz range is also accomodated when an external TTL
compatible clock is applied to XTAL1 as the frequency
source.
The I/O Circuit
WRENB
LQ
Pn
DB
D
SD
RES
RDENB
P1, P3
MV20556
Specifications subject to change without notice, contact your sales representatives for the most recent information.
18/27
PID256** 07/97