P89LPC920FDH PHILIPS [NXP Semiconductors], P89LPC920FDH Datasheet - Page 19

• Manufacturer Part Number: P89LPC920FDH
• Description: 8-bit microcontrollers with two-clock 80C51 core 2 kB/4 kB/8 kB 3 V low-power Flash with 256-byte data RAM
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
9397 750 12285
Product data
8.12.2 Quasi-bidirectional output configuration
8.12.3 Open-drain output configuration
8.12.4 Input-only configuration
8.12.5 Push-pull output configuration
8.12.6 Port 0 analog functions
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 P89LPC920/921/922 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
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
An open-drain port pin has a Schmitt-triggered input that also has a glitch
suppression circuit.
The input-only port configuration has no output drivers. It is a Schmitt-triggered input
that also has a glitch suppression circuit.
The push-pull output configuration has the same pull-down structure as both the
open-drain and the quasi-bidirectional output modes, but provides a continuous
strong pull-up when the port latch contains a logic ‘1’. The push-pull mode may be
used when more source current is needed from a port output. A push-pull port pin
has a Schmitt-triggered input that also has a glitch suppression circuit.
The P89LPC920/921/922 incorporates two Analog Comparators. In order to give the
best analog function performance and to minimize power consumption, pins that are
being used for analog functions must have the digital outputs and digital inputs
disabled.
Digital outputs are disabled by putting the port output into the Input-Only (high
impedance) mode as described in
Digital inputs on Port 0 may be disabled through the use of the PT0AD register,
bits 1:5. On any reset, PT0AD1:5 defaults to ‘0’s to enable digital functions.
Rev. 06 — 21 November 2003
DD
, causing extra power consumption. Therefore, applying
8-bit microcontrollers with two-clock 80C51 core
Section
DD
.
P89LPC920/921/922
8.12.4.
© Koninklijke Philips Electronics N.V. 2003. All rights reserved.
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