AD5272 datasheet(21/28 Pages) AD

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Data Sheet

AD5272/AD5274

Rev. D | Page 21 of 28

RDAC REGISTER

The RDAC register directly controls the position of the digital

rheostat wiper. For example, when the RDAC register is loaded

with all zeros, the wiper is connected to Terminal A of the

variable resistor. It is possible to both write to and read from

the RDAC register using the I2C interface. The RDAC register

is a standard logic register; there is no restriction on the number

of changes allowed.

50-TP MEMORY BLOCK

The AD5272/AD5274 contain an array of 50-TP programmable

memory registers, which allow the wiper position to be pro-

grammed up to 50 times. Table 16 shows the memory map.

Command 3 in Table 12 programs the contents of the RDAC

Location 0x01, see Table 16, and the AD5272/AD5274 incre-

ments the 50-TP memory address for each subsequent program

until the memory is full. Programming data to 50-TP consumes

approximately 4 mA for 55 ms, and takes approximately 350 ms

to complete, during which time the shift register is locked pre-

venting any changes from taking place. Bit C3 of the control

command was successful. No change in supply voltage is required

to program the 50-TP memory; however, a 1 µF capacitor on

the EXT_CAP pin is required as shown in Figure 47.

Prior to 50-TP activation, the AD5272/AD5274 is preset to

midscale on power-up. It is possible to read back the contents

of any of the 50-TP memory registers through the I2C interface

by using Command 5 in Table 12. The lower six LSB bits, D0 to

D5 of the data byte, select which memory location is to be read

back. A binary encoded version address of the most recently

programmed wiper memory location can be read back using

Command 6 in Table 12. This can be used to monitor the spare

memory status of the 50-TP memory block.

WRITE PROTECTION

On power-up, serial data input register write commands for

both the RDAC register and the 50-TP memory registers are

disabled. The RDAC write protect bit (Bit C1) of the control

disables any change of the RDAC register content regardless of

the software commands, except that the RDAC register can be

refreshed from the 50-TP memory using the software reset,

Command 4, or through hardware by the RESET pin. To enable

programming of the variable resistor wiper position (programming

the RDAC register), the write protect bit (Bit C1) of the control

loading the serial data input register with Command 7 (see

Table 12). To enable programming of the 50-TP memory block,

Bit C0 of the control register, which is set to 0 by default, must

first be set to 1.

Table 12. Command Operation Truth Table

Command

Number

Command[DB13:DB10]

Data[DB9:B0]1

Operation

NOP: do nothing.

D12

D02

Write contents of serial register

data to RDAC.

Read contents of RDAC wiper

Store wiper setting: store RDAC

setting to 50-TP.

Software reset: refresh RDAC

with the last 50-TP memory

stored value.

Read contents of 50-TP from the

SDO output in the next frame.

Read address of the last 50-TP

programmed memory location.

Write contents of the serial

Read contents of the control

Software shutdown.

D0 = 0; normal mode.

D0 = 1; shutdown mode.

X = don’t care.

AD5274 = don’t care.

See Table 16 for the 50-TP memory map.

See Table 15 for bit details.

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