AT89LP51RB2 datasheet(72/254 Pages) ATMEL

72 / 254 page

3722A–MICRO–10/11

AT89LP51RB2/RC2/IC2 Preliminary

12.1.3

Open-drain Output

The open-drain output configuration turns off all pull-ups and only drives the pull-down transistor

of the port pin when the port latch contains a logic “0”. To be used as a logic output, a port con-

figured in this manner must have an external pull-up, typically a resistor tied to V

DD. The pull-

down for this mode is the same as for the quasi-bidirectional mode. The open-drain port configu-

ration is shown in Figure 12-4. The input circuitry of P3.2, P3.3, P4.6 and P4.7 is not disabled

during Power-down (see Figure 12-3) and therefore these pins should not be left floating during

Power-down when configured in this mode.

Figure 12-4. Open-Drain Output

12.1.4

Push-pull Output

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. The push-pull port configuration is shown in Figure 12-5.

Figure 12-5. Push-pull Output

12.2

Port Analog Functions

The AT89LP51RB2/RC2/IC2 incorporates two analog comparators and an 8-channel analog-to-

digital converter. In order to give the best analog performance and minimize power consump-

tion, pins that are being used for analog functions must have both their digital outputs and digital

inputs disabled. Digital outputs are disabled by putting the port pins into the input-only mode as

described in “Port Configuration” on page 69. The analog input pins will always default to input-

only mode after reset regardless of the state of the Tristate-Port Fuse.

Port

From Port

Input

Data

PWD

Port

VCC

From Port

Input

Data

PWD

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