P89LPC913 datasheet(34/66 Pages) NXP

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P89LPC912_913_914_5

Product data sheet

Rev. 05 — 28 September 2007

34 of 66

NXP Semiconductors

P89LPC912/913/914

8-bit microcontrollers with two-clock 80C51 core

[1]

Required for operation above 12 MHz.

The P89LPC914 has three I/O ports: Port 0, Port 1, and Port 2. The exact number of I/O

pins available depends upon the reset option chosen, as shown in Table 11.

[1]

Required for operation above 12 MHz.

8.12.1 Port conﬁgurations

Except as listed below, every I/O pin on the P89LPC912/913/914 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/T0 may only be conﬁgured to be either input-only or open drain (P89LPC912,

P89LPC914).

8.12.2 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 P89LPC912/913/914 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.

Table 10.

Number of I/O pins available (P89LPC912, P89LPC913)

Clock source

Reset option

Number of

I/O pins

(14-pin

package)

On-chip oscillator or watchdog

oscillator

No external reset (except during power-up)

External RST pin supported

External clock input

No external reset (except during power-up)

External RST pin supported

Low/medium/high-speed oscillator

(external crystal or resonator)

No external reset (except during power-up)

External RST pin supported[1]

Table 11.

Number of I/O pins available (P89LPC914)

Reset option

Number of I/O pins

(14-pin package)

No external reset (except during power-up)

External RST pin supported[1]

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