w78l812a Winbond Electronics Corp America, w78l812a Datasheet - Page 8

• Manufacturer Part Number: w78l812a
• Description: 8-bit Mcu Series 80c51-based
• Manufacturer: Winbond Electronics Corp America

5.3
The Port 0 and Port 3 of W78L812 may be configured with different types by setting the bits of the
Port Options Register POR that is located at 86H. The pins of Port 0 can be configured with either the
open drain or standard port with internal pull-up. By the default, Port 0 is an open drain bi-directional
I/O port. When the PUP bit in the POR register is set, the pins of Port 0 will perform a quasi-bi-
directional I/O port with internal pull-up that is structurally the same as Port 2. The high nibble of Port 3
(P3.4 to P3.7) can be selected to serve the direct LED displays drive outputs by setting the HDx bit in
the PO register. When the HDx bit is set, the corresponding pin P3.x can sink about 20mA current for
driving LED display directly. After reset, the POR register is cleared and the pins of Ports 0 and 3 are
the same as those of the standard 80C31. The POR register is shown below.
5.3.1
PUP
HD4 − 7: Enable pins P3.4 to P3.7 individually with High Drive outputs.
EP6
5.4
The W78L812 has one additional bit-addressable I/O port P4 in which the port address is D8H. The
Port 4 contains seven bits; P4.0 to P4.3 are only available on 44-pin PLCC/QFP package; P4.6 is the
alternate function corresponding to pin PSEN . When program is running in the internal memory
without any access to external memory, PSEN may be individually configured to the alternate
functions P4.6 that serve as general purpose I/O pins. To enable I/O port P4.6, the bit EP6 in the POR
register must be set. During reset, the, PSEN perform as in the standard 80C32. The alternate
functions P4.6 must be enabled by software. Care must be taken with the ALE pins when configured
as the alternate functions.
5.4.1
I/O Port Options
Port 4
Port Options Register
: Enable P4.6. To set this bit shifts PSEN pin to the alternate function P4.6
Port 4
: Enable Port 0 weak pull-up.
Bit:
Bit:
EP6
7
7
-
Mnemonic: POR
Mnemonic: P4
P4.6
6
6
-
5
5
-
-
HD7
- 8 -
4
4
-
HD6
P4.3
Address: D8H
3
3
Address: 86H
W78LE812/W78L812A
P4.2
HD5
2
2
HD4
P4.1
1
1
PUP
P4.0
0
0