P89LPC938 NXP Semiconductors, P89LPC938 Datasheet - Page 24

• Manufacturer Part Number: P89LPC938
• Description: The P89LPC938 is a single-chip microcontroller, available in low cost packages, based ona high performance processor architecture that executes instructions in two to four clocks,six times the rate of standard 80C51 devices
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Table 7:
[1]
9397 750 14051
Product data sheet
Clock source
On-chip oscillator or watchdog oscillator
External clock input
Low/medium/high speed oscillator
(external crystal or resonator)
Required for operation above 12 MHz.
Number of I/O pins available
7.13.1.1 Quasi-bidirectional output configuration
7.13.1.2 Open-drain output configuration
7.13.1 Port configurations
7.13 I/O ports
The P89LPC938 has four I/O ports: Port 0, Port 1, Port 2, and Port 3. Ports 0, 1and 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
All but three I/O port pins on the P89LPC938 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 P89LPC938 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
extra power consumption. Therefore, applying 5 V in quasi-bidirectional mode is
discouraged.
A quasi-bidirectional port pin has a Schmitt triggered 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
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
.
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
Rev. 01 — 25 February 2005
8-bit microcontroller with 10-bit A/D converter
[1]
[1]
Table
7.
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
P89LPC938
Number of I/O pins
(28-pin package)
26
25
25
24
24
23
DD
, causing
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