ATAR080 datasheet(22/68 Pages) ATMEL

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ATAR080

4675D–4BMCU–12/04

Bi-directional Ports

Ports 2, 4 and 5 are 4 bits wide. All ports may be used for data input or output. All ports

are equipped with Schmitt trigger inputs and a variety of mask options for open-drain,

open-source, full-complementary outputs, pull-up and pull-down transistors. All Port

Data Registers (PxDAT) are I/O mapped to the primary address register of the respec-

tive port address and the Port Control Register (PxCR), to the corresponding auxiliary

There are three different directional ports available:

Port 2 -

4-bit wide bitwise programmable I/O port.

Port 5 -

4-bit wide bitwise programmable bi-directional port with optional static

pull-ups and programmable interrupt logic.

Port 4 -

4-bit wide bitwise programmable bi-directional port also provides the I/O

interface to Timer 2, SSI, voltage monitor input and external interrupt input.

Bi-directional Port 2

This, and all other bi-directional ports include a bitwise programmable Control Register

(P2CR), which enables the individual programming of each port bit as input or output. It

also opens up the possibility of reading the pin condition when in output mode. This is a

useful feature for self-testing and for serial bus applications

Port 2 however, has an increased drive capability and an additional low resistance pull-

up/-down transistor mask option.

Care should be taken connecting external components to BP20/NTE. During any reset

phase, the BP20/NTE input is driven towards V

DD by an additional internal strong pull-up

transistor. This pin must not be pulled down (active or passive) to V

SS during reset by

any external circuitry representing a resistor of less than 150 k

Ω. This prevents the cir-

cuit from unintended switching to test mode enable through the application circuitry at

pin BP20/NTE. Resistors less than 150 k

Ω might lead to an undefined state of the inter-

nal test logic thus disabling the application firmware.

To avoid any conflict with the optional internal pull-down transistors, BP20 handles the

pull-down options in a different way than all other ports. BP20 is the only port that

switches off the pull-down transistors during reset.

Figure 22. Bi-directional Port 2

Master reset

BP2y

(1) Mask options

(1)

P2DATy

P2CRy

I/O Bus

Pull-up

Pull-down

Static

Pull-up

(Data out)

(Direction)

Static

Pull-down

(1)

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