MCP433X datasheet(39/88 Pages) MICROCHIP

39 / 88 page

 2010 Microchip Technology Inc.

DS22242A-page 39

MCP433X/435X

4.0

FUNCTIONAL OVERVIEW

This data sheet covers a family of four volatile Digital

Potentiometer and Rheostat devices that will be

referred to as MCP43XX. The MCP43X1 devices are

the Potentiometer configuration, while the MCP43X2

devices are the Rheostat configuration.

As the Device Block Diagram shows, there are four

main functional blocks. These are:

• POR/BOR and Reset Operation

• Memory Map

• Resistor Network

• Serial Interface (SPI)

The POR/BOR operation and the Memory Map are

discussed in this section and the Resistor Network and

SPI operation are described in their own sections. The

Device Commands are discussed in Section 7.0.

4.1

POR/BOR and Reset Operation

The Power-on Reset is the case where the device is

having power applied to it from VSS. The Brown-out

Reset occurs when a device had power applied to it,

and that power (voltage) drops below the specified

range.

The devices RAM retention voltage (VRAM) is lower

than the POR/BOR voltage trip point (VPOR/VBOR). The

maximum VPOR/VBOR voltage is less than 1.8V.

When VPOR/VBOR < VDD < 2.7V, the analog electrical

performance

may

not

meet

the

data

sheet

specifications. In this region, the device is capable of

incrementing, decrementing, reading and writing to its

volatile memory, if the proper serial command is

executed.

When VDD < VPOR/VBOR or the RESET pin is Low, the

pin weak pull-ups are enabled.

4.1.1

POWER-ON RESET

When the device powers up, the device VDD will cross

the VPOR/VBOR voltage. Once the VDD voltage crosses

the VPOR/VBOR voltage, the following happens:

• Volatile wiper register is loaded with the default

value

• The TCON registers are loaded with their default

value

• The device is capable of digital operation

4.1.2

BROWN-OUT RESET

When the device powers down, the device VDD will

cross the VPOR/VBOR voltage.

Once the VDD voltage decreases below the VPOR/VBOR

voltage the following happens:

• Serial Interface is disabled

If the VDD voltage decreases below the VRAM voltage,

the following happens:

• Volatile wiper registers may become corrupted

• TCON registers may become corrupted

As the voltage recovers above the VPOR/VBOR voltage,

the operation is the same as Power-on Reset (see

Section 4.1.1 “Power-on Reset”).

Serial commands not completed due to a brown-out

condition may cause the memory location to become

corrupted.

4.1.3

RESET PIN

The RESET pin can be used to force the device into

the POR/BOR state of the device. When the RESET

pin is forced Low, the device is forced into the Reset

state. This means that the TCON registers are forced

to their default values and the volatile wiper registers

are loaded with the default value. Also the SPI

interface is disabled.

This feature allows a hardware method for all registers

to be updated to the default value at the same time.

4.1.4

INTERACTION OF RESET PIN AND BOR/

POR CIRCUITRY

Figure 4-1 shows how the RESET pin signal and the

POR/BOR signal interact to control the hardware Reset

state of the device.

FIGURE 4-1:

POR/BOR Signal and

RESET Pin Interaction.

RESET (from pin)

POR/BOR signal

Device Reset

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