Low-Power, 16-Bit Smart ADC

12

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There are three internal DSP registers that are directly

observable on the SDIO and SDO pins:

• S: 16-bit DSP Scratch or Accumulator register, con-

taining the result of the execution of the current

microcode instruction.

• P: 8-bit DSP Program Pointer register, which holds

the address of the instruction ROM microcode.

• PS: 8-bit DSP Program Store register. PS is the

instruction that the DSP is currently executing. PS is

the instruction ROM data at address P.

The DSP instructions relevant to the test system are list-

ed in Table 8.

After the test system sends the Start Conversion com-

mands 8 hex or A hex, SDIO and SDO are both

enabled as MAX1460 serial outputs. The test system

should disable (high impedance) its SDIO driver to

avoid a bus conflict at this time so that the MAX1460

can drive the pin. After the DSP executes each one of

the microcode instructions, the contents of the registers

S, P, and PS are output in a serial format (Figure 4).

A new DSP instruction and a new state of the S, P, and

PS registers are delivered every 16n + 9 clock cycles,

where n = 0, 1, 2... after the Start Conversion command

completes. The tester should latch the SDIO and SDO

0F

MSB

Configuration

LSB

0D

0E

1F

MSB

0B

Gain

LSB

EE Address (hex)

10

1D

09

Contents

1E

0A

1B

EE Address (hex)

20

19

Contents

1A

0C

1C

18

16

08

17

14

12

06

13

15

11

07

2F

MSB

04

LSB

2D

02

2E

03

3F

MSB

05

2B

LSB

01

EE Address (hex)

30

3D

29

Contents

3E

2A

3B

EE Address (hex)

40

39

Contents

3A

2C

3C

38

36

28

37

34

32

26

33

35

31

27

24

22

23

25

21

4F

MSB

LSB

4D

4E

5F

MSB

4B

LSB

EE Address (hex)

50

5D

49

Contents

5E

4A

5B

EE Address (hex)

60

59

Contents

5A

4C

5C

58

56

48

57

54

52

46

53

55

51

47

6F

MSB

44

LSB

6D

42

6E

43

7F

MSB

45

6B

LSB

41

EE Address (hex)

70

7D

69

Contents

7E

6A

7B

EE Address (hex)

00

79

Contents

7A

6C

7C

78

76

68

77

74

72

66

73

75

71

67

64

62

63

65

61

Table 7. EEPROM Memory Map

D7

Register 8—Temperature

Signal

Register 0—Configuration

56

Register 9—Sensor Signal

D8

01

D9

Register 1—Gain

3B

Register 10—Compensated

Output D

D0

66 or 6C

EA

65 or 6B

D1

47

D2

11

D3

2E

D4

38

D5

03

D6

22

INSTRUCTION

CODE (PS)

(HEX)

S REGISTER VALUE

PROGRAM

COUNTER

(P)

(HEX)

Table 8. Subset of DSP Instruction