Bus operations
M29W640GH, M29W640GL, M29W640GT, M29W640GB
3.5
Automatic Standby
If CMOS levels (V
0.2V) are used to drive the bus and the bus is inactive for 300ns or
CC
more the memory enters Automatic Standby where the internal Supply Current is reduced to
the Standby Supply Current, I . The Data Inputs/Outputs will still output data if a Bus
CC2
Read operation is in progress.
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 V to be
ID
applied to some pins.
3.6.1
3.6.2
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 7:
Bus Operations, BYTE = V and Table 8: Bus Operations, BYTE = V , with A9 set to V .
IL
IH
ID
Block Protect and Chip Unprotect
Groups of blocks can be protected against accidental Program or Erase. The Protection
Groups are shown in Appendix A: Block addresses Table 28 and Table 29. The whole chip
can be unprotected to allow the data inside the blocks to be changed.
The V /Write Protect pin can be used to protect the two outermost blocks on the
PP
M29W640GH and M29W640GL, and the four outermost blocks on the M29W640GT and
M29W640GB. When V /Write Protect is at V the outermost blocks are protected and
PP
IL
remain protected regardless of the Block Protection Status or the Reset/Block Temporary
Unprotect pin status.
Block Protect and Chip Unprotect operations are described in : Revision history.
20/90
NUMONYX [ NUMONYX B.V ]
