P89LPC913 datasheet(33/63 Pages) PHILIPS

33 / 63 page

Philips Semiconductors

P89LPC912/913/914

8-bit microcontrollers with two-clock 80C51 core

Product data

Rev. 03 — 17 December 2004

33 of 63

9397 750 14468

A quasi-bidirectional port pin has a Schmitt-triggered input that also has a glitch

suppression circuit.

9.11.3

Open-drain output conﬁguration

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 VDD.

An open-drain port pin has a Schmitt-triggered input that also has a glitch

suppression circuit.

9.11.4

Input-only conﬁguration

The input-only port conﬁguration has no output drivers. It is a Schmitt-triggered input

that also has a glitch suppression circuit.

9.11.5

Push-pull output conﬁguration

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.

9.11.6

Port 0 analog functions

The P89LPC912/913/914 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 Section 9.11.4 “Input-only conﬁguration”.

Digital inputs on Port 0 may be disabled through the use of the PT0AD register. On

any reset, the PT0AD bits default to ‘0’s to enable digital functions.

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