The AT26DF321 also offers a sophisticated method for protecting individual sectors against
erroneous or malicious program and erase operations. By providing the ability to individually pro-
tect and unprotect sectors, a system can unprotect a specific sector to modify its contents while
keeping the remaining sectors of the memory array securely protected. This is useful in applica-
tions where program code is patched or updated on a subroutine or module basis, or in
applications where data storage segments need to be modified without running the risk of errant
modifications to the program code segments. In addition to individual sector protection capabili-
ties, the AT26DF321 incorporates Global Protect and Global Unprotect features that allow the
entire memory array to be either protected or unprotected all at once. This reduces overhead
during the manufacturing process since sectors do not have to be unprotected one-by-one prior
to initial programming.
Specifically designed for use in 3-volt systems, the AT26DF321 supports read, program, and
erase operations with a supply voltage range of 2.7V to 3.6V. No separate voltage is required for
programming and erasing.
2. Pin Descriptions and Pinouts
Table 2-1. Pin Descriptions
Name and Function
CHIP SELECT: Asserting the CS pin selects the device. When the CS pin is deasserted, the
device will be deselected and normally be placed in standby mode (not Deep Power-Down mode),
and the SO pin will be in a high-impedance state. When the device is deselected, data will not be
accepted on the SI pin.
A high-to-low transition on the CS pin is required to start an operation, and a low-to-high transition
is required to end an operation. When ending an internally self-timed operation such as a program
or erase cycle, the device will not enter the standby mode until the completion of the operation.
SERIAL CLOCK: This pin is used to provide a clock to the device and is used to control the flow of
data to and from the device. Command, address, and input data present on the SI pin is always
latched on the rising edge of SCK, while output data on the SO pin is always clocked out on the
falling edge of SCK.
SERIAL INPUT: The SI pin is used to shift data into the device. The SI pin is used for all data input
including command and address sequences. Data on the SI pin is always latched on the rising
edge of SCK.
SERIAL OUTPUT: The SO pin is used to shift data out from the device. Data on the SO pin is
always clocked out on the falling edge of SCK.
WRITE PROTECT: The WP pin controls the hardware locking feature of the device. Please refer to
“Protection Commands and Features” on page 11 for more details on protection features and the
The WP pin is internally pulled-high and may be left floating if hardware controlled protection will
not be used. However, it is recommended that the WP pin also be externally connected to VCC
DEVICE POWER SUPPLY: The VCC pin is used to supply the source voltage to the device.
Operations at invalid VCC voltages may produce spurious results and should not be attempted.
GROUND: The ground reference for the power supply. GND should be connected to the system