W39L512

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The manufacturer and device codes may also be read via the command register, for instance, when

the W39L512 is erased or programmed in a system without access to high voltage on the A9 pin. The

command sequence is illustrated in "Auto-select Codes".

device identifier code (W39L512 = 38H). All identifiers for manufacturer and device will exhibit odd

parity with DQ7 defined as the parity bit. In order to read the proper device codes when executing the

Auto-select, A1 must be low state.

Data Protection

The W39L512 is designed to offer protection against accidental erasure or programming caused by

spurious system level signals that may exist during power transitions. During power up the device

automatically resets the internal state machine in the Read mode. Also, with its control register

architecture, alteration of the memory contents only occurs after successful completion of specific

multi-bus cycle command sequences. The device also incorporates several features to prevent

Boot Block Operation

There are two alternatives to set the boot block. The 8K-byte in the top/bottom location of this device

can be locked as boot block, which can be used to store boot codes. It is located in the last 8K bytes or

first 8K bytes of the memory with the address range from E000(hex) to FFFF(hex) for top location or

0000(hex) to 1FFF(hex) for bottom location.

See Command Codes for Boot Block Lockout Enable for the specific code. Once this feature is set the

data for the designated block cannot be erased or programmed (programming lockout), other memory

locations can be changed by the regular programming method.

In order to detect whether the boot block feature is set on the first/last 8K-byte block or not, users can

perform software command sequence: enter the product identification mode (see Command Codes for

Identification/Boot Block Lockout Detection for specific code), and then read from address 0002(hex)

for first(bottom) location or FFF2(hex) for last(top) location.

If the DQ0/DQ1 of output data is "1,"

the 8Kbytes boot block programming lockout feature will be activated; if the DQ0/DQ1 of output data is

"0," the lockout feature will be inactivated and the block can be erased/programmed.

To return to normal operation, perform a three-byte command sequence (or an alternate single-byte

command) to exit the identification mode. For the specific code, see Command Codes for

Identification/Boot Block Lockout Detection.

prevent unintentional writes.

Write Pulse "Glitch" Protection

Noise pulses of less than 10 nS (typical) on #OE, #CE, or #WE will not initiate a write cycle.