W29C020C

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sequence is required. For information about specific codes, see the Command Codes for Software

Data Protection in the Table of Operating Modes. For information about timing waveforms, see the

timing diagrams below.

Hardware Data Protection

The integrity of the data stored in the W29C020C is also hardware protected in the following ways:

(1) Noise/Glitch Protection: A WE pulse of less than 15 nS in duration will not initiate a write cycle.

prevents inadvertent writes during power-up or power-down periods.

5 mS before any write (erase/program) operation.

Chip Erase Modes

The entire device can be erased by using a six-byte software command code. See the Software Chip

Erase Timing Diagram.

Boot Block Operation

There are two boot blocks (8K bytes each) in this device, which can be used to store boot code. One

of them is located in the first 8K bytes and the other is located in the last 8K bytes of the memory.

The first 8K or last 8K of the memory can be set as a boot block by using a seven-byte command

sequence.

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. Once the boot block

programming lockout feature is activated, the chip erase function will be disabled. In order to detect

whether the boot block feature is set on the two 8K blocks, users can perform a six-byte command

sequence: enter the product identification mode (see Command Codes for Identification/Boot Block

Lockout Detection for specific code), and then read from address "00002 hex" (for the first 8K bytes)

or "3FFF2 hex" (for the last 8K bytes). If the output data is "FF hex," the boot block programming

lockout feature is activated; if the output data is "FE hex," the lockout feature is deactivated and the

block can be programmed.

To return to normal operation, perform a three-byte command sequence to exit the identification

mode. For the specific code, see Command Codes for Identification/Boot Block Lockout Detection.

Data Polling (DQ7)- Write Status Detection

The W29C020C includes a data polling feature to indicate the end of a write cycle. When the

W29C020C is in the internal write cycle, any attempt to read DQ7 from the last byte loaded during the

page/byte-load cycle will receive the complement of the true data. Once the write cycle is completed.

DQ7 will show the true data. See the OE Polling Timing Diagram.