P89LPC9321FN NXP Semiconductors, P89LPC9321FN Datasheet - Page 27

• Manufacturer Part Number: P89LPC9321FN
• Description: MCU 8-Bit 89LP 80C51 CISC 8KB Flash 2.5V/3.3V 28-Pin PDIP Tube
• Manufacturer: NXP Semiconductors

NXP Semiconductors
P89LPC9321_1
Product data sheet
7.16.1.1 Quasi-bidirectional output configuration
7.16.1.2 Open-drain output configuration
7.16.1 Port configurations
7.16 I/O ports
The P89LPC9321 has four I/O ports: Port 0, Port 1, Port 2 and Port 3. Ports 0, 1, and 2
are 8-bit ports, and Port 3 is a 2-bit port. The exact number of I/O pins available depends
upon the clock and reset options chosen, as shown in
Table 7.
All but three I/O port pins on the P89LPC9321 may be configured by software to one of
four types on a bit-by-bit basis. These are: quasi-bidirectional (standard 80C51 port
outputs), push-pull, open drain, and input-only. Two configuration registers for each port
select the output type for each port pin.
Quasi-bidirectional output type can be used as both an input and output without the need
to reconfigure the port. This is possible because when the port outputs a logic HIGH, it is
weakly driven, allowing an external device to pull the pin LOW. When the pin is driven
LOW, it is driven strongly and able to sink a fairly large current. These features are
somewhat similar to an open-drain output except that there are three pull-up transistors in
the quasi-bidirectional output that serve different purposes.
The P89LPC9321 is a 3 V device, but the pins are 5 V-tolerant. In quasi-bidirectional
mode, if a user applies 5 V on the pin, there will be a current flowing from the pin to V
causing extra power consumption. Therefore, applying 5 V in quasi-bidirectional mode is
discouraged.
A quasi-bidirectional port pin has a Schmitt trigger input that also has a glitch suppression
circuit.
The open-drain output configuration turns off all pull-ups and only drives the pull-down
transistor of the port driver when the port latch contains a logic 0. To be used as a logic
output, a port configured in this manner must have an external pull-up, typically a resistor
tied to V
Clock source
On-chip oscillator or watchdog
oscillator
External clock input
Low/medium/high speed
oscillator (external crystal or
resonator)
1. P1.5 (RST) can only be an input and cannot be configured.
2. P1.2 (SCL/T0) and P1.3 (SDA/INT0) may only be configured to be either input-only or
open-drain.
DD
.
Number of I/O pins available
Rev. 01 — 9 December 2008
8-bit microcontroller with accelerated two-clock 80C51 core
Reset option
No external reset (except during
power-up)
External RST pin supported
No external reset (except during
power-up)
External RST pin supported
No external reset (except during
power-up)
External RST pin supported
Table
7.
P89LPC9321
© NXP B.V. 2008. All rights reserved.
Number of I/O
pins (28-pin
package)
26
25
25
24
24
23
27 of 70
DD
,