Rainbow-electronics AT89LP214 Manual de usuario descargar pdf (Pagina 24)

3538A–MICRO–7/06

AT89LP213/214 [Preliminary]

13.1.2 Input-only Mode

The input only port configuration is shown in Figure 13-2. The output drivers are tristated. The

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

P1.3, P3.2 and P3.3 is not disabled during Power-down (see Figure 13-3). Input pins can be

safely driven to 5.5V even when operating at lower V

levels; however, the input threshold of

the Schmitt trigger will be set by the V

level and must be taken into consideration.

Figure 13-2. Input Only

Figure 13-3. Input Only for P1.3, P3.2 and P3.3

13.1.3 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

. 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 13-4.The input circuitry of P1.3, P3.2 and P3.3 is not disabled during

Power-down (see Figure 13-3). Open-drain pins can be safely pulled high to 5.5V even when

operating at lower V

levels; however, the input threshold of the Schmitt trigger will be set by

the V

level and must be taken into consideration.

Figure 13-4. Open-drain Output

13.1.4 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 13-5. The input circuitry of

P1.3, P3.2 and P3.3 is not disabled during Power-down (see Figure 13-3).

Port

Input

Data

PWD

Port

Input

Data

Port

From Port

Input

Data

PWD

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