AD5175

Rev. 0 | Page 16 of 20

RDAC REGISTER

The RDAC register directly controls the position of the digital

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

with all 0s, the wiper is connected to Terminal A of the variable

resistor. It is possible to both write to and read from the RDAC

logic register; there is no restriction on the number of changes

allowed.

50-TP MEMORY BLOCK

The AD5175 contains an array of 50-TP programmable

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

grammed up to 50 times. Table 11 shows the memory map.

Command 3 in Table 7 programs the contents of the RDAC

register to memory. The first address to be programmed is

Location 0x01, see Table 11, and the AD5175 increments 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 preventing any changes from taking place. Bit C2 of

the control register in Table 10 can be polled to verify that the

fuse program 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 29.

Prior to 50-TP activation, the AD5175 presets to midscale on

power-up. It is possible to read back the contents of any of the

Command 5 in Table 7. 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 pro-

grammed wiper memory location can be read back using

Command 6 in Table 7. 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

register (see Table 9 and Table 10), is set to 0 by default. This

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 the 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 register must first be programmed.

This is accomplished by loading the serial data input register

with Command 7 (see

). 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 7

Table 7. Command Operation Truth Table

Command

Number

Command[DB13:DB10]

Data[DB9:DB0]1

C3

C2

C1

C0

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

Operation

0

0

0

0

0

X

X

X

X

X

X

X

X

X

X

NOP: do nothing.

1

0

0

0

1

D9

D8

D7

D6

D5

D4

D3

D2

D1

D

Write contents of serial register data

to RDAC.

2

0

0

1

0

X

X

X

X

X

X

X

X

X

X

Read contents of RDAC wiper register.

3

0

0

1

1

X

X

X

X

X

X

X

X

X

X

Store wiper setting: store RDAC setting

to 50-TP.

4

0

1

0

0

X

X

X

X

X

X

X

X

X

X

Software reset: refresh RDAC with the

last 50-TP memory stored value.

52

0

1

0

1

X

X

X

X

D5

D4

D3

D2

D1

D0

Read contents of 50-TP from the SDO

output in the next frame.

6

0

1

1

0

X

X

X

X

X

X

X

X

X

X

Read address of the last 50-TP

programmed memory location.

73

0

1

1

1

X

X

X

X

X

X

X

X

D1

D0

Write contents of the serial register data

to the control register.

8

1

0

0

0

X

X

X

X

X

X

X

X

X

X

Read contents of the control register.

9

1

0

0

1

X

X

X

X

X

X

X

X

X

D0

Software shutdown.

D0 = 0; normal mode.

D0 = 1; shutdown mode.

2 See Table 11 for the 50-TP memory map.