Datasheet

© 2009 Microchip Technology Inc. DS22233A-page 31
MCP434X/436X
4.0 FUNCTIONAL OVERVIEW
This Data Sheet covers a family of four non-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 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 V
SS
. 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 (V
RAM
) is lower
than the POR/BOR voltage trip point (V
POR
/V
BOR
). The
maximum V
POR
/V
BOR
voltage is less then 1.8V.
When V
POR
/V
BOR
< V
DD
< 2.7V, the electrical
performance may not meet the data sheet
specifications. In this region, the device is capable of
reading and writing to its EEPROM and incrementing,
decrementing, reading and writing to its volatile
memory if the proper serial command is executed.
When V
DD
< V
POR
/V
BOR
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 V
DD
will cross
the V
POR
/V
BOR
voltage. Once the V
DD
voltage crosses
the V
POR
/V
BOR
voltage, the following happens:
• Volatile wiper register is loaded with value in the
corresponding non-volatile wiper register
• The TCON registers are loaded their default value
• The device is capable of digital operation
4.1.2 BROWN-OUT RESET
When the device powers down, the device V
DD
will
cross the V
POR
/V
BOR
voltage.
Once the V
DD
voltage decreases below the V
POR
/V
BOR
voltage the following happens:
• Serial Interface is disabled
• EEPROM Writes are disabled
If the V
DD
voltage decreases below the V
RAM
voltage,
the following happens:
• Volatile wiper registers may become corrupted
• TCON registers may become corrupted
As the voltage recovers above the V
POR
/V
BOR
voltage
see Section 4.1.1 “Power-on Reset”.
Serial commands not completed due to a brown-out
condition may cause the memory location (volatile and
non-volatile) 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 and STATUS
registers are forced to their default values and the
volatile wiper registers are loaded with the value in the
corresponding Non-Volatile wiper register. Also the
SPI interface is disabled. Any non-volatile write cycle
is not interrupted, and allowed to complete.
This feature allows a hardware method for all registers
to be updated 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