at49bv642dt ATMEL Corporation, at49bv642dt Datasheet - Page 3

• Manufacturer Part Number: at49bv642dt
• Description: 64-megabit 4m X 16 3-volt Only Flash Memory
• Manufacturer: ATMEL Corporation

3. Device Operation
3.1
3.2
3.3
3.4
3.4.1
3.4.2
3631A–FLASH–04/06
Command Sequences
Read
Reset
Erase
Chip Erase
Sector Erase
The device powers on in the read mode. Command sequences are used to place the device in
other operating modes such as program and erase. After the completion of a program or an
erase cycle, the device enters the read mode. The command sequences are written by applying
a low pulse on the WE input with CE low and OE high or by applying a low-going pulse on the
CE input with WE low and OE high. The address is latched on the falling edge of the WE or CE
pulse whichever occurs first. Valid data is latched on the rising edge of the WE or the CE pulse,
whichever occurs first. The addresses used in the command sequences are not affected by
entering the command sequences.
The AT49BV642D(T) is accessed like an EPROM. When CE and OE are low and WE is high,
the data stored at the memory location determined by the address pins are asserted on the out-
puts. The outputs are put in the high impedance state whenever CE or OE is high. This dual-line
control gives designers flexibility in preventing bus contention.
A RESET input pin is provided to ease some system applications. When RESET is at a logic
high level, the device is in its standard operating mode. A low level on the RESET pin halts the
present device operation and puts the outputs of the device in a high-impedance state. When a
high level is reasserted on the RESET pin, the device returns to read or standby mode, depend-
ing upon the state of the control pins.
Before a word can be reprogrammed it must be erased. The erased state of the memory bits is a
logical “1”. The entire memory can be erased by using the Chip Erase command or individual
sectors can be erased by using the Sector Erase command.
Chip Erase is a six-bus cycle operation. The automatic erase begins on the rising edge of the
last WE pulse. Chip Erase does not alter the data of the protected sectors. After the full chip
erase the device will return back to the read mode. The hardware reset during Chip Erase will
stop the erase but the data will be of unknown state. Any command during Chip Erase except
Erase Suspend will be ignored.
As an alternative to a full chip erase, the device is organized into multiple sectors that can be
individually erased. The Sector Erase command is a six-bus cycle operation. The sector whose
address is valid at the sixth falling edge of WE will be erased provided the given sector has not
been protected.
AT49BV642D(T)
3