AD1816A

–41–

REV. A

PLUG AND PLAY KEY AND “ALTERNATE KEY” SEQUENCES

One additional feature of the AD1816A is an alternate programming method used, for example, if a BIOS wants to assume control

of the AD1816A and present DEVNODES to the OS (rather than having the device participate in Plug and Play enumeration). The

following technique may be used.

Instead of the normal 32 byte Plug and Play key sequence, an alternate 126 byte key is used. After the 126 byte key, the AD1816A

device will transition to the Plug and Play “sleep” state. It can then be programmed as usual using the standard Plug and Play ports.

After programming, the AD1816A should be sent to the Plug and Play “WFK” (wait for key) state. Once the AD1816A has seen the

alternate key, it will no longer parse for the Plug and Play key (and therefore never participate in Plug and Play enumeration). It can

be reprogrammed by reissuing the alternate key again.

Both the Plug and Play key and the alternate key are sequences of writes to the Plug and Play address register, 0x279. Below are the

ISA data values of both keys.

This is the standard Plug and Play sequence:

6a

b5

da

ed

f6

fb

7d

be

df

6f

37

1b

0d

86

c3

61

b0

58

2c

16

8b

45

a2

d1

e8

74

3a

9d

ce

e7

73

39

This is the longer, 126-byte alternate key. It is generated by the function:

f[n+1] = (f[n] >> 1)| (((f[n] ^ (f[n] >> 1)) & 0x01) << 6) f[0] = 0x01

01

40

20

10

08

04

02

41

60

30

18

0c

06

43

21

50

28

14

0a

45

62

71

78

3c

1e

4f

27

13

09

44

22

51

68

34

1a

4d

66

73

39

5c

2e

57

2b

15

4a

65

72

79

7c

3e

5f

2f

17

0b

05

42

61

70

38

1c

0e

47

23

11

48

24

12

49

64

32

59

6c

36

5b

2d

56

6b

35

5a

6d

76

7b

3d

5e

6f

37

1b

0d

46

63

31

58

2c

16

4b

25

52

69

74

3a

5d

6e

77

3b

1d

4e

67

33

19

4c

26

53

29

54

2a

55

6a

75

7a

7d

7e

7f

3f

1f

0f

07