
June 28, 2004 S25FL004D_00A0
S25FL Family (Serial Peripheral Interface) S25FL004D
7
Ad va nc e
In forma t i o n
Signal Description
Signal Data Output (SO): This output signal is used to transfer data serially out
of the device. Data is shifted out on the falling edge of Serial Clock (SCK).
Serial Data Input (SI): This input signal is used to transfer data serially into
the device. It receives instructions, addresses, and the data to be programmed.
Values are latched on the rising edge of Serial Clock (SCK).
Serial Clock (SCK): This input signal provides the timing of the serial interface.
Instructions, addresses, and data present at the Serial Data input (SI) are latched
on the rising edge of Serial Clock (SCK). Data on Serial Data Output (SO) changes
after the falling edge of Serial Clock (SCK).
Chip Select (CS#): When this input signal is High, the device is deselected and
Serial Data Output (SO) is at high impedance. Unless an internal Program, Erase
or Write Status Register cycle is in progress, the device will be in Standby mode.
Driving Chip Select (CS#) Low enables the device, placing it in the active power
mode.
After Power-up, a falling edge on Chip Select (CS#) is required prior to the start
of any instruction.
Hold (HOLD#): The Hold (HOLD#) signal is used to pause any serial communi-
cations with the device without deselecting the device.
During the Hold instruction, the Serial Data Output (SO) is high impedance, and
Serial Data Input (SI) and Serial Clock (SCK) are Don’t Care.
To start the Hold condition, the device must be selected, with Chip Select (CS#)
driven Low.
Write Protect (W#): The main purpose of this input signal is to freeze the size
of the area of memory that is protected against program or erase instructions (as
specified by the values in the BP1 and BP0 bits of the Status Register).
SPI Modes
These devices can be driven by a microcontroller with its SPI peripheral running
in either of the two following modes:
CPOL = 0, CPHA = 0
CPOL = 1, CPHA = 1
For these two modes, input data is latched in on the rising edge of Serial Clock
(SCK), and output data is available from the falling edge of Serial Clock (SCK).
The difference between the two modes, as shown in
Figure 2, is the clock polarity
when the bus master is in Standby and not transferring data:
SCK remains at 0 for (CPOL = 0, CPHA = 0)
SCK remains at 1 for (CPOL = 1, CPHA = 1)