AD1821 Analog Devices, AD1821 Datasheet - Page 41

• Manufacturer Part Number: AD1821
• Manufacturer: Analog Devices

PLUG AND PLAY KEY AND “ALTERNATE KEY” SEQUENCES
One additional feature of the AD1821 is an alternate programming method used, for example, if a BIOS wants to assume control of
the AD1821 and present DEVNODES to the OS (rather than having the device participate in Plug and Play enumeration). The fol-
lowing 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 AD1821
device will transition to the Plug and Play “config” state. It can then be programmed as usual using the standard Plug and Play ports.
After programming, the AD1821 should be sent to the Plug and Play “WFK” (wait for key) state. Once the AD1821 has seen the al-
ternate 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
b0
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
28
68
7c
48
76
52
29
REV. 0
b5
58
40
14
34
3e
24
7b
69
54
da
2c
20
0a
1a
5f
12
3d
74
2a
ed
16
10
45
4d
2f
49
5e
3a
55
f6
8b
08
62
66
17
64
6f
5d
6a
fb
45
04
71
73
0b
32
37
6e
75
7d
a2
02
78
39
05
59
1b
77
7a
be
d1
41
3c
5c
42
6c
0d
3b
7d
APPENDIX B
–41–
df
e8
60
1e
2e
61
36
46
1d
7e
6f
74
30
4f
57
70
5b
63
4e
7f
37
3a
18
27
2b
38
2d
31
67
3f
1b
9d
0c
13
15
1c
56
58
33
1f
0d
ce
06
09
4a
0e
6b
2c
19
0f
86
e7
43
44
65
47
35
16
4c
07
AD1821
c3
73
21
22
72
23
5a
4b
26
61
39
50
51
79
11
6d
25
53