Bus operations
M29W800DT, M29W800DB
3.6
Special bus operations
Additional bus operations can be performed to read the electronic signature and also to
apply and remove block protection. These bus operations are intended for use by
programming equipment and are not usually used in applications. They require VID to be
applied to some pins.
3.6.1
Electronic signature
The memory has two codes, the manufacturer code and the device code, that can be read
to identify the memory. These codes can be read by applying the signals listed in Table 2
and Table 3, Bus operations.
3.6.2 Block protection and blocks unprotection
Each block can be separately protected against accidental program or erase. Protected
blocks can be unprotected to allow data to be changed.
There are two methods available for protecting and unprotecting the blocks, one for use on
programming equipment and the other for in-system use. Block protect and chip unprotect
operations are described in Appendix C: Block protection.
Table 2. Bus operations, BYTE = VIL(1)
Operation
E
G
W
Address inputs
DQ15A–1, A0-A18
Data inputs/outputs
DQ14-DQ8
DQ7-DQ0
Bus read
VIL VIL VIH Cell address
Bus write
VIL VIH VIL Command address
Output disable
X
VIH VIH X
Standby
VIH
X
XX
Read manufacturer code VIL
VIL
VIH
A0 = VIL, A1 = VIL, A9 =
VID, others VIL or VIH
Read device code
VIL
VIL
VIH
A0 = VIH, A1 = VIL, A9 =
VID, others VIL or VIH
1. X = VIL or VIH.
Table 3. Bus operations, BYTE = VIH (1)
Operation
E
G
W
Address inputs
A0-A18
Hi-Z
Data output
Hi-Z
Data input
Hi-Z
Hi-Z
Hi-Z
Hi-Z
Hi-Z
20h
D7h (M29W800DT)
Hi-Z
5Bh (M29W800DB)
Data inputs/outputs
DQ15A–1, DQ14-DQ0
Bus read
VIL
VIL
VIH Cell address
Data output
Bus write
VIL
VIH
VIL Command address
Data input
Output disable
X
VIH
VIH X
Hi-Z
Standby
VIH
X
XX
Hi-Z
Read manufacturer code VIL
VIL
VIH
A0 = VIL, A1 = VIL, A9 = VID,
others VIL or VIH
0020h
Read device code
VIL
VIL
VIH
A0 = VIH, A1 = VIL, A9 = VID,
others VIL or VIH
22D7h (M29W800DT)
225Bh (M29W800DB)
1. X = VIL or VIH.
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