Avago Technologies LSI53C1020 - Manual (Page 113)

I/O Space and Memory Space Register Descriptions 4-35
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Register: 0x04
Write Sequence
Read/Write
The Write Sequence register provides a protection mechanism against
inadvertent writes to the Host Diagnostic register.
Reserved [31:4]
This field is reserved.
Write I/O Key [3:0]
To enable write access to the Diagnostic Read/Write
Data , Diagnostic Read/Write Address , and Host Diagnos-
tic registers, perform five data-specific writes to the Write
I/O Key. Writing an incorrect value to the Write I/O Key
invalidates the key sequence, and the host must rewrite
the entire sequence. The Write I/O Key sequence is:
0x0004, 0x000B, 0x0002, 0x0007, and 0x000D. To dis-
able write access to the
Diagnostic Read/Write Data ,
Diagnostic Read/Write Address , and Host Diagnostic reg-
isters, perform a write of any value, except the Write I/O
Key sequence, to the Write Sequence register. The Diag-
nostic Write Enable bit, bit 7 in the
Host Diagnostic reg-
ister, indicates the write access status.
31 4 3 0
Write Sequence
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 1