MCP4921 datasheet(23/50 Pages) MICROCHIP

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 2010 Microchip Technology Inc.

DS22248A-page 23

MCP4901/4911/4921

5.0

SERIAL INTERFACE

5.1

Overview

The MCP4901/4911/4921 devices are designed to

interface directly with the Serial Peripheral Interface

(SPI) port, which is 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 on the rising edge of SCK. The

communications are unidirectional, thus the data

cannot be read out of the MCP4901/4911/4921. 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.

ter that is used to configure and load the DAC register

for each device. Figure 5-1 through Figure 5-3 show

the write command for each device.

Refer to Figure 1-1 and the 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 DAC’s input register.

The MCP4901/4911/4921 utilizes a double-buffered

latch structure to allow the analog output to be

synchronized with the LDAC pin, if desired.

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

tent stored in the DAC’s input register is transferred into

the DAC’s output register (VOUT), and VOUT is updated.

All writes to the MCP4901/4911/4921 devices are

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

ignored. The Most Significant 4 bits are Configuration

bits. The remaining 12 bits are data bits. No data can

be transferred into the device with CS high. This

transfer will only occur if 16 clocks have been

transferred into the device. If the rising edge of CS

occurs prior to that, shifting of data into the input

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