MCP4921 datasheet(21/50 Pages) MICROCHIP

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DS20002249B-page 21

MCP4802/4812/4822

5.0

SERIAL INTERFACE

5.1

Overview

The MCP4802/4812/4822 devices are designed to

interface directly with the Serial Peripheral Interface

(SPI) port, available on many microcontrollers, and

supports Mode 0,0 and Mode 1,1. Commands and data

are sent to the device via the SDI pin, with data being

clocked-in

the

rising

edge

SCK.

The

communications are unidirectional and, thus, data

cannot be read out of the MCP4802/4812/4822

devices. The CS pin must be held low for the duration

of a write command. The write command consists of

16 bits and is used to configure the DAC’s control and

data latches. Register 5-1 to Register 5-3 detail the

input register that is used to configure and load the

DACA and DACB registers for each device. Figure 5-1

to Figure 5-3 show the write command for each device.

Refer to Figure 1-1 and SPI Timing Specifications

Table for detailed input and output timing specifications

for both Mode 0,0 and Mode 1,1 operation.

5.2

Write Command

The write command is initiated by driving the CS pin

low, followed by clocking the four Configuration bits and

the 12 data bits into the SDI pin on the rising edge of

SCK. The CS pin is then raised, causing the data to be

latched into the selected DAC’s input registers.

The MCP4802/4812/4822 devices utilize a double-

buffered latch structure to allow both DACA’s and

DACB’s outputs to be synchronized with the LDAC pin,

if desired.

By bringing down the LDAC pin to a low state, the con-

tents stored in the DAC’s input registers are transferred

into the DAC’s output registers (VOUT), and both VOUTA

and VOUTB are updated at the same time.

All writes to the MCP4802/4812/4822 devices are

16-bit words. Any clocks after the first 16th clock will be

ignored.

The

Most

Significant

four

bits

are

Configuration bits. The remaining 12 bits are data bits.

No data can be transferred into the device with CS

high. The data transfer will only occur if 16 clocks have

been transferred into the device. If the rising edge of

CS occurs prior, shifting of data into the input registers

will be aborted.

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