P89LPC934 PHILIPS [NXP Semiconductors], P89LPC934 Datasheet - Page 30

• Manufacturer Part Number: P89LPC934
• Description: 8-bit microcontroller with accelerated two-clock 80C51 core 4 kB/8 kB 3 V byte-erasable Flash with 8-bit A/D converters
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
9397 750 15113
Product data sheet
8.13.1.1 Quasi-bidirectional output configuration
8.13.1.2 Open-drain output configuration
8.13.1 Port configurations
8.13 I/O ports
The P89LPC933/934/935/936 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 8:
[1]
All but three I/O port pins on the P89LPC933/934/935/936 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 P89LPC933/934/935/936 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
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
Required for operation above 12 MHz.
open-drain.
DD
.
Number of I/O pins available
DD
, causing extra power consumption. Therefore, applying 5 V in
Rev. 06 — 20 June 2005
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
P89LPC933/934/935/936
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
[1]
[1]
Number of I/O pins
(28-pin package)
26
25
25
24
24
23
Table
8.
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