Datasheet

 2008-2013 Microchip Technology Inc. DS22096B-page 35
MCP453X/455X/463X/465X
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 (I
2
C)
The POR/BOR operation and the memory map are
discussed in this section and the Resistor Network and
I
2
C operation are described in their own sections. The
Device Commands commands are discussed in
Section 7.0 “Device Commands”.
4.1 POR/BOR Operation
The Power-on Reset is the case where the device has
power applied to it, starting from the V
SS
level. The
Brown-out Reset occurs when power is applied to the
device, and that power (voltage) drops below the spec-
ified range.
The device’s 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 than 1.8V.
When V
POR
/V
BOR
<V
DD
< 2.7V, the electrical perfor-
mance may not meet the data sheet specifications. In
this region, the device is capable of incrementing, dec-
rementing, 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
(mid-scale)
• The TCON register is loaded with the 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 Serial Interface is disabled.
If the V
DD
voltage decreases below the V
RAM
voltage,
the following may happen:
• Volatile wiper registers become corrupt
• TCON register becomes corrupt
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 volatile memory location to
become corrupted.
4.2 Memory Map
The device memory map supports 16 locations, of
which three locations are used. Each location is 9-bits
wide (16x9 bits). This memory space is shown in
Table 4-1.
TABLE 4-1: MEMORY MAP
4.2.1 VOLATILE MEMORY (RAM)
There are four volatile memory locations. These are:
• Volatile Wiper 0
• Volatile Wiper 1
(Dual Resistor Network devices only)
• Terminal Control (TCON) register
• Reserved
The volatile memory starts functioning at the RAM
retention voltage (V
RAM
).
4.2.1.1 Address 05h (Reserved)
This memory location is Reserved and is mapped to
the Status Register of the nonvolatile MCP45XX/46XX
devices. Since the nonvolatile device’s bits are not
used by the volatile device, this location is reserved.
Reading this address will result in a value of 1F7h.
Address Function Memory Type
00h Volatile Wiper 0 RAM
01h Volatile Wiper 1 RAM
02h Reserved —
03h Reserved —
04h Volatile TCON register RAM
05h Reserved RAM
06h - 0Fh Reserved —