Casio EX-I/O-PB-12, Service Manual

Page: 12 / 33

— 10 —
Pin No. Name In/Out Status Status Status Description
of OFF of ON of ON
No token Token
20 INTR Out L H Pulse
21 CS In L H Pulse
22 WR/DIR In L Pulse Pulse
23 RD/DS In L L Pulse
24 VCC Power GND +5V +5V
Interrupt output. This active low signal
is generated by the COM20020 when
an enabled interrupt condition occurs.
INTR returns to its inactive state when
the interrupt status condition or the
corresponding interrupt mask bit is
reset.
Chip select input. This active low
signal issued by the microcontroller
selects the COM20020 for an access.
Input. On a 68XX-like bus, this signal
is issued by the microcontroller as the
Read/Write signal to determine the
direction of data transfer. In this case,
a logic "1" selects a read operation,
while a logic "0" selects a write
operation. In this case, data is
actually strobed by the DS signal. On
an 80XX-like bus, this active low
signal is isuued by the microcontroller
to indicate a write operation. in this
case, a logic "0" on this pin, when the
COM20020 is accessed, enables data
from the data bus to be written to the
device.
Read/ Data strobe signal input. On a
68XX-like bus, this active low signal is
issued by the microcontroller as the
data strobe signal to strobe the data
onto the bus. On a 80XX-like bus, this
active low signal is issued by the
microcontroller to indicate a read
operation. In this case, a logic "0" on
this pin, when the COM20020 is
accessed, enables data from the
device to the data bus to be read by
the microcontroller.
Power 5V.
CS
WR/DIR
RD/DS
INTR