AT89LP428 datasheet(37/149 Pages) ATMEL

37 / 149 page

3654A–MICRO–8/09

AT89LP428/828

10.1.2

Input-only Mode

The input only port configuration is shown in Figure 10-2. The output drivers are tristated. The

input includes a Schmitt-triggered input for improved input noise rejection. The input circuitry of

P3.2, P3.3, P3.6, P4.0 and P4.1 is not disabled during Power-down (see Figure 10-3) and there-

fore these pins should not be left floating during Power-down when configured in this mode.

Figure 10-2. Input Only

Figure 10-3. Input Circuit for P3.2, P3.3 and P3.6

10.1.3

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

CC. 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 10-4. The input circuitry of P3.2, P3.3 and P3.6 is not disabled during

Power-down (see Figure 10-3) and therefore these pins should not be left floating during Power-

down when configured in this mode.

Figure 10-4. Open-drain Output

Port

Input

Data

PWD

Port

Input

Data

Port

From Port

Input

Data

PWD

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