AD5258

Data Sheet

Rev. D | Page 18 of 24

TOLERANCE READBACK MODES

Table 15. Traditional Readback of Tolerance (Individually)

S

7-Bit Device Address

(See Table 5)

0 SA 0 0 1 1 1 1 1 0 SA S

7-Bit Device Address

(See Table 5)

1 SA D7 D6 D5 D4 D3 D2 D1 D0 NA P

Slave Address Byte

Instruction Byte

Slave Address Byte

Sign + Integer Byte

↑

Repeat Start

S

7-Bit Device Address

(See Table 5)

0 SA 0 0 1 1 1 1 1 1 SA S

7-Bit Device Address

(See Table 5)

1 SA D7 D6 D5 D4 D3 D2 D1 D0 NA P

Slave Address Byte

Instruction Byte

Slave Address Byte

Decimal Byte

↑

Repeat Start

Table 16. Traditional Readback of Tolerance (Consecutively)

S

7-Bit Device Address

(See Table 5)

0 SA 0 0 1 1 1 1 1 0 SA S

7-Bit Device Address

(See Table 5)

1 SA D7 D6 D5 D4 D3 D2 D1 D0 MA D7 D6 D5 D4 D3 D2 D1 D0 NA P

Slave Address Byte

Instruction Byte

Slave Address Byte

Sign + Integer Byte

Decimal Byte

↑

Repeat Start

A

A

A

D7

D6

D5

D4

D3

D2

D1

D0

SIGN

SIGN

SEVEN BITS FOR AN INTEGER NUMBER

D7

D6

D5

D4

D3

D2

D1

D0

EIGHT BITS FOR A DECIMAL NUMBER

Figure 39. Format of Stored Tolerance in Sign Magnitude Format with Bit Position Descriptions

(Unit is Percent; Only Data Bytes are Shown)

nonvolatile memory. Tolerance is stored in the memory during

factory production and can be read by users at any time. The

knowledge of stored tolerance allows users to accurately calcu-

and open-loop applications where knowledge of absolute

resistance is critical.

The stored tolerance resides in the read-only memory and is

expressed as a percentage. The tolerance is stored in two memory

location bytes in sign magnitude binary form (see Figure 39). The

two EEPROM address bytes are 11110 (sign + integer) and 11111

(decimal number). The two bytes can be individually accessed

with two separate commands (see Table 15). Alternatively, read-

back of the first byte followed by the second byte can be done

in one command (see Table 16). In the latter case, the memory

pointer automatically increments from the first to the second

EEPROM location (increments from 11110 to 11111) if read

consecutively.

In the first memory location, the MSB is designated for the sign

(0 = + and 1 = −) and the seven LSBs are designated for the integer

portion of the tolerance. In the second memory location, all eight

data bits are designated for the decimal portion of tolerance. Note

that the decimal portion has a limited accuracy of only 0.1%. For

Address 11110 shows 0001 1100 and from Address 11111 shows

0000 1111, the tolerance can be calculated as

MSB: 0 = +

Next 7 MSB: 001 1100 = 28

Tolerance = 28.06%

Rounded Tolerance = 28.1% and therefore