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AT29C020 Datasheet(PDF) 4 Page - ATMEL Corporation

Part No. AT29C020
Description  2-Megabit 256K x 8 5-volt Only CMOS Flash Memory
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Manufacturer  ATMEL [ATMEL Corporation]
Direct Link  http://www.atmel.com
Logo ATMEL - ATMEL Corporation

AT29C020 Datasheet(HTML) 4 Page - ATMEL Corporation

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shipped from Atmel, the software data protection feature is disabled. To enable the software
data protection, a series of three program commands to specific addresses with specific data
must be performed. After the software data protection is enabled the same three program com-
mands must begin each program cycle in order for the programs to occur. All software program
commands must obey the sector program timing specifications. Once set, the software data pro-
tection feature remains active unless its disable command is issued. Power transitions will not
reset the software data protection feature; however, the software feature will guard against inad-
vertent program cycles during power transitions.
After setting SDP, any attempt to write to the device without the 3-byte command sequence will
start the internal write timers. No data will be written to the device; however, for the duration of
WC, a read operation will effectively be a polling operation.
After the software data protection’s 3-byte command code is given, a sector of data is loaded
into the device using the sector program timing specifications.
Hardware Data Protection
Hardware features protect against inadvertent programs to the AT29C020 in the following ways:
(a) V
CC sense – if VCC is below 3.8V (typical), the program function is inhibited; (b) VCC power on
delay – once V
CC has reached the VCC sense level, the device will automatically time out 5 ms
(typical) before programming; (c) Program inhibit – holding any one of OE low, CE high or WE
high inhibits program cycles; and (d) Noise filter – pulses of less than 15 ns (typical) on the WE
or CE inputs will not initiate a program cycle.
Product Identification
The product identification mode identifies the device and manufacturer as Atmel. It may be
accessed by hardware or software operation. The hardware operation mode can be used by an
external programmer to identify the correct programming algorithm for the Atmel product.
In addition, users may wish to use the software product identification mode to identify the part
(i.e. using the device code), and have the system software use the appropriate sector size for
program operations. In this manner, the user can have a common board design for 256K to
4-megabit densities and, with each density’s sector size in a memory map, have the system soft-
ware apply the appropriate sector size.
For details, see Operating Modes (for hardware operation) or Software Product Identification.
The manufacturer and device code is the same for both modes.
DATA Polling
The AT29C020 features DATA polling to indicate the end of a program cycle. During a program
cycle an attempted read of the last byte loaded will result in the complement of the loaded data
on I/O7. Once the program cycle has been completed, true data is valid on all outputs and the
next cycle may begin. DATA polling may begin at any time during the program cycle.
Toggle Bit
In addition to DATA polling the AT29C020 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.

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