This Data Sheet may be revised by subsequent versions

©2004 Eon Silicon Solution, Inc.,

www.eonssi.com

or modifications due to changes in technical specifications.

6

EN25S40

Rev. A, Issue Date: 2009/04/28

OPERATING FEATURES

Standard SPI Modes

The EN25S40 is accessed through an SPI compatible bus consisting of four signals: Serial Clock (CLK),

Chip Select (CS#), Serial Data Input (DI) and Serial Data Output (DO). Both SPI bus operation Modes 0

(0,0) and 3 (1,1) are supported. The primary difference between Mode 0 and Mode 3, as shown in

Figure 3, concerns the normal state of the CLK signal when the SPI bus master is in standby and data

is not being transferred to the Serial Flash. For Mode 0 the CLK signal is normally low. For Mode 3 the

CLK signal is normally high. In either case data input on the DI pin is sampled on the rising edge of the

CLK. Data output on the DO pin is clocked out on the falling edge of CLK.

Figure 3. SPI Modes

Dual SPI Instruction

The EN25S40 supports Dual SPI operation when using the “ Dual Output Fast Read and Dual I/ O

FAST_READ “ (3Bh and BBh) instructions. These instructions allow data to be transferred to or from

the Serial Flash memory at two to three times the rate possible with the standard SPI. The Dual Read

instructions are ideal for quickly downloading code from Flash to RAM upon power-up (code-shadowing)

or for application that cache code-segments to RAM for execution. The Dual output feature simply

allows the SPI input pin to also serve as an output during this instruction. When using Dual SPI

the standard SPI interface with single output signal.

Page Programming

To program one data byte, two instructions are required: Write Enable (WREN), which is one byte, and

a Page Program (PP) sequence, which consists of four bytes plus data. This is followed by the internal

To spread this overhead, the Page Program (PP) instruction allows up to 256 bytes to be programmed

at a time (changing bits from 1 to 0) provided that they lie in consecutive addresses on the same page

of memory.

Sector Erase, Block Erase and Chip Erase

The Page Program (PP) instruction allows bits to be reset from 1 to 0. Before this can be applied, the

bytes of memory need to have been erased to all 1s (FFh). This can be achieved a sector at a time,

using the Sector Erase (SE) instruction, a block at a time using the Block Erase (BE) instruction or

throughout the entire memory, using the Chip Erase (CE) instruction. This starts an internal Erase cycle

instruction.

Polling During a Write, Program or Erase Cycle

A further improvement in the time to Write Status Register (WRSR), Program (PP) or Erase (SE, BE or

Progress (WIP) bit is provided in the Status Register so that the application program can monitor its

value, polling it to establish when the previous Write cycle, Program cycle or Erase cycle is complete.