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AT29C010A

4.8

Toggle Bit

In addition to DATA polling the AT29C010A provides another method for determining the end of

a program or erase cycle. During a program or erase operation, successive attempts to read

data from the device will result in I/O6 toggling between one and zero. Once the program cycle

has completed, I/O6 will stop toggling and valid data will be read. Examining the toggle bit may

begin at any time during a program cycle.

4.9

Optional Chip Erase Mode

The entire device can be erased by using a 6-byte software code. Please see Software Chip

Erase application note for details.

4.10

Boot Block Programming Lockout

The AT29C010A has two designated memory blocks that have a programming lockout feature.

This feature prevents programming of data in the designated block once the feature has been

enabled. Each of these blocks consists of 8K bytes; the programming lockout feature can be set

independently for either block. While the lockout feature does not have to be activated, it can be

activated for either or both blocks.

These two 8K memory sections are referred to as boot blocks. Secure code which will bring up a

system can be contained in a boot block. The AT29C010A blocks are located in the first 8K

bytes of memory and the last 8K bytes of memory. The boot block programming lockout feature

can therefore support systems that boot from the lower addresses of memory or the higher

addresses. Once the programming lockout feature has been activated, the data in that block can

no longer be erased or programmed; data in other memory locations can still be changed

through the regular programming methods. To activate the lockout feature, a series of seven

program commands to specific addresses with specific data must be performed. Please see

Boot Block Lockout Feature Enable Algorithm.

If the boot block lockout feature has been activated on either block, the chip erase function will

be disabled.

4.10.1

Boot Block Lockout Detection

A software method is available to determine whether programming of either boot block section is

locked out. See Software Product Identification Entry and Exit sections. When the device is in

the software product identification mode, a read from location 00002 will show if programming

the lower address boot block is locked out while reading location 1FFF2 will do so for the upper

boot block. If the data is FE, the corresponding block can be programmed; if the data is FF, the

program lockout feature has been activated and the corresponding block cannot be pro-

grammed. The software product identification exit mode should be used to return to standard

operation.