MV20556 Datasheet, PDF (16/30 Pages) Mosel Vitelic, Corp – 8 - Bit MCU Mouse Controller

MOSEL VITELIC INC.
Preliminary
MV20556
External Interface
Reset
Processor initialization is accomplished with acitivation
of the RES pin. To reset the processor, this pin should
be held high for at least twenty-four oscillator periods.
Upon powering up, RES should be held high for at least
1 ms after the power supply stabilizes to allow the
oscillator to stabilize. Upon receipt of RES, the
processor ceases instruction execution and remains
dormant for the duration of the pulse. The pins assume
their initialization states within 2 machine cycles clocks.
The low-going transition then initiates a sequence
which requires approximately twelve oscillator periods
to execute before ALE(internal signal) is generated and
normal operation commences with the instruction at
absolute location 0000H. This sequence ends with
registers initialized as shown in right table.
When the processor is reset all ports are immediately
written with ones (1's).
MV20556
30µF
RES
R_RES
Power-on Reset
1K ohm
MV20556
RES
R_RES
The Schimitt-trigger input has a small internal pull down
resistor which permits power-on reset (as shown in
right to Figure) using only a small capacitor tied to
VDD. A conventional external reset circuit, such as
that in right Figure, can also be used.
1K _ohm
30µF
RES
MV20556
R_RES
I OL
Output low current.
For port 1 and port 3, MV20556 provided I OL up to
18mA per pin typicallly at VOL=0.45V. User are free to
choose any one of these 15 pins to perform this high
current sink capability. But they are restricted: no more
than 80 mA I OLs for all output pins.
External Reset
Content after
Content after
Register
Reset at Power on Reset while running
PC
0000H
0000H
SP
07H
07H
PSW
00H
00H
DPH, DPL 00H
00H
A, B
00H
00H
IP
E0H or 00H
E0H or 00H
IE
60H or 00H
60H or 00H
SCON
00H
00H
TMOD
00H
00H
TCON
00H
00H
TH1, TH0 00H
00H
TL1, TL0
00H
00H
SBUF
indeterminate
indeterminate
Port 1 & 3 FFH (*1)
FFH (*1)
Internal RAM indeterminate
unchanged
*1 configures all i/o pins as inputs
Specifications subject to change without notice, contact your sales representatives for the most recent information.
16/27
Register vs Reset
PID256** 07/97