VSC056 datasheet(79/134 Pages) MAXIM

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VSC056

Data Sheet

Revision 4.1

January 2008

4:2

FS2-0

R/W

Function Select

These three bits, along with the PTE, DD, and GPD bits, determine the function

of each I/O pin.

When configured as an output, the FS2-0 bits determine the rate at which the

high current drive I/O toggles, providing a simple mechanism for flashing LEDs.

The DD and GPD bits can be used to drive each I/O individually and to take the

place of the byte wide controls found in the DD and GPD registers. Note that the

DD bit is always de-asserted to configure the I/O as an output. Asserting the DD

bit tri-states the I/O and effectively configures the I/O as an input. The six bits

allow the user to select one of seven flash rates or eight user-programmable

pulse trains, as well as to drive the LED both on and off. The output can be

enabled to drive in an open-source (output drives to VDD with an external pull-

down resistor) or open-drain (output drives to VSS with an external pull-up)

configuration when using the flashing mechanism. For available combinations to

drive an LED, see Table 5, page 80.

When configured as an input, the DD bit is asserted. These bits determine the

type of I/O pin edge transition that generates an interrupt condition. Transition

detectors within the device filter the changes observed at the I/O pin and

determine if a valid transition has occurred. If a valid transition occurs, the INT#

pin asserts and a binary value equal to the address of this register appears in

the BCIS register. For available input edge combinations, see Table 6, page 81.

Note: When configuring an I/O pin from an output to an input with interrupt

enabled, it is recommended that the data direction change and interrupt

enabling be accomplished with separate register write operations. This

guarantees that any I/O transition that occurs as a result of the data direction

change, which may rely on the weak internal pull-up resistor, does not generate

an unexpected interrupt.

R/W

Data Direction

This bit determines the direction of the data flow through the I/O pin.

To enable the respective I/O pin as an input, set the appropriate bit.

To enable the respective I/O pin as an output, reset the appropriate bit.

Each I/O pin can be individually configured as a true bidirectional function. To

implement an open-drain or open-source function, set or reset the appropriate

data bit using the data direction bit as the programmed data value.

After a reset or power on, these bits are set to a binary 1, enabling the

I/O as an input with weak pull-up.

GPD

R/W

General-Purpose Data

When the I/O pin has been enabled as an output, writing this bit determines the

data value that is present on the corresponding I/O pin.

If the I/O pin is enabled as an input, reading this register bit represents the

current voltage applied to the pin. At no time does this bit directly represent the

value latched into the data register.

If the pin is enabled as an input and there is no signal applied, a weak internal

pull-up resistor holds the pin at a binary 1. After a reset or power on, this

is the level applied to the pin since each pin is an input by default.

Bit

Bit Label

Access

Description

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