89LPC925 datasheet(24/49 Pages) PHILIPS

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Philips Semiconductors

P89LPC924/925

8-bit microcontrollers with accelerated two-clock 80C51 core

Product data

Rev. 03 — 15 December 2004

24 of 49

9397 750 14471

8.13.1

Port conﬁgurations

All but three I/O port pins on the P89LPC924/925 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.

P1.5 (RST) can only be an input and cannot be conﬁgured.

P1.2 (SCL/T0) and P1.3 (SDA/INT0) may only be conﬁgured to be either input-only or

open-drain.

8.13.2

Quasi-bidirectional output conﬁguration

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 P89LPC924/925 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 VDD, causing 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.

8.13.3

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.

8.13.4

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.

8.13.5

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.

8.13.6

Port 0 analog functions

The P89LPC924/925 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.

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