Rainbow-electronics ATAR862-8 User Manual download pdf (Page 34)

ATAR862-8

4589B–4BMCU–02/03

Figure 29. Bi-directional Port 1

Bi-directional Port 2 As all other bi-directional ports, this port includes a bitwise programmable Control Reg-

ister (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

by an additional internal strong pull-up

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

during reset by

any external circuitry representing a resistor of less than 150 kW. This prevents the cir-

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

pin BP20/NTE. Resistors less than 150 kW 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 30. Bi-directional Port 2

OUT

Reset

I/O Bus

Master reset

P1DATy

(Data out)

(Direction)

BP1y

Switched

pull-up

*) Mask options

Static

pull-up

Static

pull-down

Switched

pull-down

Master reset

BP2y

Mask options

P2DATy

P2CRy

I/O Bus

Switched

pull-up

Static

Pull-up

(Data out)

(Direction)

Static

Pull-down

Switched

pull-down

1 2 ... 29 30 31 32 33 34 35 36 37 38 39 ... 105 106

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Rainbow-electronics ATAR862-8 User Manual Page 34

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