![](http://datasheet.mmic.net.cn/90000/ML66Q525-NTB_datasheet_3507944/ML66Q525-NTB_127.png)
ML66525 Family User’s Manual
Chapter 5
Port Functions
5 - 22
5.7
Port 3 (P3)
Port 3 is a 3-bit I/O port. Each individual bit can be specified as input or output by the port 3
mode register (P3IO).
When output is specified (corresponding bits of P3IO = “1”), the value
of the corresponding bits in the port 3 data register (P3) will be output from their appropriate
pins.
In addition to its port function, P3 is assigned secondary functions (PSENn, RDn, and WRn
outputs).
If a secondary function is to be used, set the corresponding bits of the port 3 mode
register (P3IO) and the port 3 secondary function control register (P3SF) to “1”.
If the port is specified as an input (corresponding bits of P3IO = “0”) and the port 3 secondary
function control register (P3SF) is set to “1”, the pin inputs corresponding to those bits will be
pulled-up.
Bit 2 of port 3 is a read-only port.
Be sure to set bit 2 (PO3IO2) of P3IO to “1” by programming.
Figure 5-9 shows the configuration of the port 3 data register (P3), port 3 mode register (P3IO)
and the port 3 secondary function control register (P3SF).
765
4
3
210
00
0
000
0/1
0
00
0
1
“—” indicates a bit that does not exist.
If read, the value will be “0”.
P3IO3 P3IO2 P3IO1
P3IO
P3SF
P3_3
P3_2
P3_1
P3
At reset
WR
P3SF3
RD
P3SF2
—
PSEN
P3SF1
——
—
——
—
765
4
3
210
765
4
3
210
00
0
000
0/1
0
1
0
1
At reset
(EAn = H/L)
At reset
(EAn = H/L)
Address: 001B [H]
R/W access: R/W
Address: 0023 [H]
R/W access: R/W
Address: 002B [H]
R/W access: R/W
Not pulled-up
P3_1 input
Primary function
P3_1 output
PSENn output
0 (Input setting)
1 (Output setting)
Pulled-up
Secondary function
Not pulled-up
Pulled-up
Inaccessible
P3_2 input
Primary function
P3_2 output
RDn output
Secondary function
Primary function
P3_3 output
WRn output
Secondary function
Figure 5-9
P3, P3IO, P3SF Configuration
[Note]
In setting bit 2 of port 3, do not select “Inaccessible”.
At reset (RESn signal input, BRK instruction execution, overflow of watchdog timer,
opcode trap), “Inaccessible” is set. Therefore, be sure to set bit 2 of P3IO to “1” by
programming.