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AS1500

7 Detailed Description

Serial-Programming

Programming of the AS150x is done via the 3 wire serial interface. The three input signals are serial data input (SDI),

clock(CK) and chip select (CSN). A programming sequence consists of 10-bit, where the last eight bit contain the code

word for the resistor value. The first two bits A1 and A0 have to be low to program the resistor value (see Table 6).

Otherwise the resistor value is not affected. The data is shifted into the internal 10 Bit register with the rising edge of

the CK signal. With the rising edge of the CSN signal the data become valid and the resistance is updated (see Figure

3). A detailed block diagram is shown in Figure 4.

Table 6. Serial data format (10 bits)

Figure 3. Timing Diagram

Figure 4. Detailed Timing Diagram

A1

A0

D7

D6

D5

D4

D3

D2

D1

D0

00

MSB

Data

LSB

A1

A0

D7

D6

D5

D4

D3

D2

D1

D0

1

0

1

0

0

1

VCC

0V

SDI

CK

CSN

DAC Register Load

1

0

1

0

0

1

0V

VCC

CSN

CK

SDI