Datasheet

© 2008 Microchip Technology Inc. DS22059B-page 29
MCP414X/416X/424X/426X
4.0 FUNCTIONAL OVERVIEW
This Data Sheet covers a family of thirty-two Digital
Potentiometer and Rheostat devices that will be
referred to as MCP4XXX. The MCP4XX1 devices are
the Potentiometer configuration, while the MCP4XX2
devices are the Rheostat configuration.
As the Device Block Diagram shows, there are four
main functional blocks. These are:
• POR/BOR 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 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.
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 register is loaded it’s 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 register 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.
4.2 Memory Map
The device memory is 16 locations that are 9-bits wide
(16x9 bits). This memory space contains both volatile
and non-volatile locations (see Table 4-1).
TABLE 4-1: MEMORY MAP
Address Function Memory Type
00h Volatile Wiper 0 RAM
01h Volatile Wiper 1 RAM
02h Non-Volatile Wiper 0 EEPROM
03h Non-Volatile Wiper 1 EEPROM
04h Volatile TCON Register RAM
05h Status Register RAM
06h Data EEPROM EEPROM
07h Data EEPROM EEPROM
08h Data EEPROM EEPROM
09h Data EEPROM EEPROM
0Ah Data EEPROM EEPROM
0Bh Data EEPROM EEPROM
0Ch Data EEPROM EEPROM
0Dh Data EEPROM EEPROM
0Eh Data EEPROM EEPROM
0Fh Data EEPROM EEPROM