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IS25F011A

1M-BIT, 2M-BIT, AND 4M-BIT SERIAL FLASH MEMORIES WITH 4-PIN SPI INTERFACE

Integrated Silicon Solution 

IS25F011A

IS25F021A

IS25F041A

ISSI ®

Read Device Information Sector

The Read Device Information command provides access

to a read-only sector that can be used to electronically

identify the ISSI Serial Flash device being interfaced to.

Information available includes: part number, density,

voltage, temperature range, package type, and any

special options. This can be extremely useful for sys-

tems that need to accommodate optional densities

1 (e.g., both 1M-bit or 4M-bit). In this case the firmware

can interrogate the Device Information Sector and de-

termine the density. The Device Information Sector also

includes a list of any restricted sectors that might exist

2 in the device. Contact ISSI for more detailed information

on the Device Information Sector format.

Read Device

Info. Sector

Byte

3

Command 16 Clocks Address* 16 Clocks

SI

15H

0000H

B[15:0]

0000H

4

SO

RB[15:0]

First Byte - Last Byte

*The byte address only uses bits [8:0]

Read/Busy

Read Sector Data

Status

5

Sector Format and Tag/Sync Bytes

The first byte of each sector is pre-programmed during

manufacturing with a tag/sync value of C9H. Although

this byte location of the sector can be changed, it is

recommended that it be maintained and incorporated

into the application’s sector formatting.

The tag/sync values serve two purposes. First, they

provide a sync-detect that can help verify if the command

sequence was clocked into the device properly. Sec-

ondly, they serve as a tag to identify a fully functional

(valid) sector. This is especially important if “restricted

sector” devices are ever to be used. Restricted sector

devices provide a more cost effective alternative to

standard devices with 100% valid sectors. Restricted

sector devices have a limited number of sectors that do

not meet manufacturing programming criteria over the

specified operating range. When such a sector is de-

tected, the first byte is tagged with a pattern other than

C9H. In addition to individual sector tagging, all restricted

sectors for a given device are listed in the Device Infor-

mation Sector. For more information see the Device

Information Sector Application Note SFAN-02.

High Data Integrity Applications

6

Data storage applications that use Flash memory or other

non-volatile media must take into consideration the possi-

bility of noise or other adverse system conditions that may

7 affect data integrity. For those applications that require

higher levels of data integrity it is a recommended practice

to use Error Correcting Code (ECC) techniques. The

IS-SFK-SPI Serial Flash Development Kit provides a

8 software routine for a 32-bit ECC that can detect up to two

bit errors and correct one. The ECC not only minimizes

problems caused by system noise but can also extend

Flash memory endurance. For those systems without the

9 processing power to handle ECC algorithms, a simple

“verification after write” is recommended. The "Compare

Sector to SRAM" command can be useful for implement-

ing this Write/Verify operation. The IS-SFK-SPI software

10 includes a simple Write/Verify routine that will compare

data written to a given sector and rewrite the sector if the

compare is not correct.

11

12

Integrated Silicon Solution, Inc.

19

PRELIMINARY SF001-1A

06/24/98

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