MCP4331T-502ESLASHML datasheet(51/88 Pages) MICROCHIP

51 / 88 page

 2010 Microchip Technology Inc.

DS22242A-page 51

MCP433X/435X

7.0

DEVICE COMMANDS

The MCP43XX’s SPI command format supports

16 memory address locations and four commands.

Each command has two modes:

• Normal Serial Commands

• High-Voltage Serial Commands

Normal serial commands are those where the CS pin is

driven to VIL. With high-voltage serial commands, the

CS pin is driven to VIHH. In each mode, there are four

possible commands. These commands are shown in

Table 7-1.

The

8-bit

commands

(Increment

Wiper

and

Decrement Wiper commands) contain a command

byte, see Figure 7-1, while 16-bit commands (Read

Data and Write Data commands) contain a command

byte and a data byte. The command byte contains two

data bits, see Figure 7-1.

Table 7-2 shows the supported commands for each

memory location and the corresponding values on the

SDI and SDO pins.

Table 7-3 shows an overview of all the SPI commands

and their interaction with other device features.

7.1

Command Byte

The command byte has three fields, the address, the

command, and 2 data bits, see Figure 7-1. Currently

only one of the data bits is defined (D8). This is for the

Write command.

The device memory is accessed when the master

sends a proper command byte to select the desired

operation. The memory location getting accessed is

contained in the command byte’s AD3:AD0 bits. The

action desired is contained in the command byte’s

C1:C0 bits, see Table 7-1. C1:C0 determines if the

desired memory location will be read, written,

incremented (wiper setting +1) or decremented (wiper

setting -1). The Increment and Decrement commands

are only valid on the volatile wiper registers.

As the command byte is being loaded into the device

(on the SDI pin), the device’s SDO pin is driving. The

SDO pin will output high bits for the first six bits of that

command. On the 7th bit, the SDO pin will output the

CMDERR

bit

state

(see

Section 7.3

“Error

Condition”). The 8th bit state depends on the

command selected.

FIGURE 7-1:

General SPI Command Formats.

TABLE 7-1:

COMMAND BIT OVERVIEW

C1:C0

Bit

States

Command

# of

Bits

Operates on

Volatile/

Nonvolatile

memory

Read Data

16-Bits Both

Write Data

16-Bits Both

Increment

8-Bits

Volatile Only

Decrement

8-Bits

Volatile Only

Memory

Command Byte

Data

Address

Bits

Command

Bits

Memory

16-bit Command

Data

Address

Bits

Command

Bits

0 0 = Write Data

0 1 = INCR

1 0 = DECR

1 1 = Read Data

C C

1 0

Command

Bits

8-bit Command

Command Byte

Data Byte

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