Port 3 (P30 - P37) - Toshiba TLCS-90 Series Data Book

TOSHIBA TMP90C840
3.5.4 Port 3 (P30 - P37)
Port 3 is an 8-bit general-purpose I/O port (P3: memory address FFC6H)
with fixed I/O function. All bits of the output latch are set to "1",
and "1" is generated to the output port.
In addition to the I/O port function, P30 - P34 have the I/O function
for the internal serial interface, while P35 - P37 have the external
memory control function. The additional functions can be selected by
the control register (P3CR: memory address FFC7H). All bits of the
control register are initialized to "0" by resetting, by which the
port turns to the general-purpose I/O port mode.
However, access of an external memorL makes P35 _-_P37 automat ically
function as the memory control pins (RD, WR and WAIT), and access of
an internal memory makes them function as general-purpose I/O ports.
When an external memory is accessed , therefore, the output latch
regis ters P35 eRD) and P36 (WR) shou ld be kept at "1" which is the
initial value after the reset.
The bit 5 (RDE) of the control
r~gister
is intended for a pseudostatic
RAM. When set to "1", it always functions as an RD pin. It is set to
"0" by reading the internal I/O unit.
Reset
Port 3 Output
(P32, P33, P35, P36)
H
~
rT
Write P3
CD
I'i
~
llJ
I-'
0
llJ
rT
llJ
tJ:l
Read P3
C
Ul
Port 3 Input
t
(P30, P31, P34, P37)
Read P3
Fig. 3.5 (6) Port 3
MPU90-61