AM29PDL127H datasheet(33/68 Pages) AMD

33 / 68 page

June 07, 2005

Am29PDL127H

P RE L I M I NARY

■

To verify the protect/unprotect status of the SecSi

Sector, follow the algorithm shown in Figure 4.

Once the SecSi Sector is locked and verified, the sys-

tem must write the Exit SecSi Sector Region com-

mand sequence to return to reading and writing the

remainder of the array.

The SecSi Sector lock must be used with caution

since, once locked, there is no procedure available for

unlocking the SecSi Sector area and none of the bits

in the SecSi Sector memory space can be modified in

any way.

SecSi Sector Protection Bits

The SecSi Sector Protection Bits prevent program-

ming of the SecSi Sector memory area. Once set, the

SecSi Sector memory area contents are non-modifi-

able.

Figure 4.

SecSi Sector Protect Verify

Hardware Data Protection

The command sequence requirement of unlock cycles

for programming or erasing provides data protection

against inadvertent writes. In addition, the following

hardware data protection measures prevent accidental

erasure or programming, which might otherwise be

caused by spurious system level signals during VCC

power-up and power-down transitions, or from system

noise.

Low VCC Write Inhibit

When VCC is less than VLKO, the device does not ac-

cept any write cycles. This protects data during VCC

power-up and power-down. The command register

and all internal program/erase circuits are disabled,

and the device resets to the read mode. Subsequent

writes are ignored until VCC is greater than VLKO. The

system must provide the proper signals to the control

pins to prevent unintentional writes when VCC is

greater than VLKO.

Write Pulse “Glitch” Protection

Noise pulses of less than 3 ns (typical) on OE#, CE#,

or WE# do not initiate a write cycle.

Logical Inhibit

Write cycles are inhibited by holding any one of OE# =

VIL, CE# = VIH or WE# = VIH. To initiate a write cycle,

CE# and WE# must be a logical zero while OE# is a

logical one.

Power-Up Write Inhibit

If WE# = CE# = VIL and OE# = VIH during power up,

the device does not accept commands on the rising

edge of WE#. The internal state machine is automati-

cally reset to the read mode on power-up.

COMMON FLASH MEMORY INTERFACE

(CFI)

The Common Flash Interface (CFI) specification out-

lines device and host system software interrogation

handshake, which allows specific vendor-specified

software algorithms to be used for entire families of

devices. Software support can then be device-inde-

pendent, JEDEC ID-independent, and forward- and

backward-compatible for the specified flash device

families. Flash vendors can standardize their existing

interfaces for long-term compatibility.

This device enters the CFI Query mode when the sys-

tem writes the CFI Query command, 98h, to address

55h, any time the device is ready to read array data.

The system can read CFI information at the addresses

given in Tables 9–12. To terminate reading CFI data,

the system must write the reset command. The CFI

Query mode is not accessible when the device is exe-

cuting an Embedded Program or embedded Erase al-

gorithm.

The system can also write the CFI query command

when the device is in the autoselect mode. The device

enters the CFI query mode, and the system can read

CFI data at the addresses given in Tables 9–12. The

system must write the reset command to return the

device to reading array data.

For further information, please refer to the CFI Specifi-

cation and CFI Publication 100, available via the World

Write 60h to

any address

Write 40h to SecSi

Sector address

with A6 = 0,

A1 = 1, A0 = 0

START

RESET# =

VIH or VID

Wait 1

μs

Read from SecSi

Sector address

with A6 = 0,

A1 = 1, A0 = 0

If data = 00h,

SecSi Sector is

unprotected.

If data = 01h,

SecSi Sector is

protected.

Remove VIH or VID

from RESET#

Write reset

command

SecSi Sector

Protect Verify

complete

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