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AN1536 APPLICATION NOTE
Designing Applications that Work with any M25Pxx Device Taking Advantage of their Hardware and Software Compatibility
CONTENTS
s s s s
Electronic Signature Number of Sectors Protected Area Sizes Bulk Erase: Time to Erase the Whole Memory Area Special Points about the M25P05-A Conclusion
One of the great advantages of the M25Pxx Serial Flash memory devices from STMicroelectronics is that all members of the family have the same footprint - all the way from the lowest end of the family (512 Kbit memory) to the highest (16 Mbit memory). As a result, the application designer can allow for any member of the family to be substituted on the circuit board. Thus one design can serve for a whole range of applications, from the lowest end of the range to the highest. There are some functional differences, though, between the individual members of the family - most of them connected to the differences in memory capacity. This application note highlights these differences. The Electronic Signature feature of the M25Pxx family (Table 1) allows the application software to identify which memory is connected on the board, and to adapt itself accordingly. Table 1. Electronic Signature
Device M25P05-A M25P10-A M25P20 M25P40 M25P80 M25P16 Electronic Signature 05h 10h 11h 12h 13h 14h
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March 2002
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AN1536 - APPLICATION NOTE
The number of bits in a sector can be 256K, for the M25P05-A and M25P10-A, or 512K, for the M25P20/ 40/80/16. The number of sectors varies according to the total memory capacity of the device (Table 2). Table 2. Number of Sectors
Device M25P05-A M25P10-A M25P20 M25P40 M25P80 M25P16 Number of Sectors 2 4 4 8 16 32 Bits per Sector 256K 256K 512K 512K 512K 512K
The number of Block Protect (BP) bits in the Status Register needs to vary, to allow for the different number of sectors in the various members of the family (Table 3 and Table 4). Table 3. Protected Area Sizes (M25P05-A, M25P10-A, M25P20)
Status Register Content BP1 Bit 0 0 1 1 BP0 Bit 0 1 0 1 none1 none (protected against Bulk Erase only)1 All M25P05-A none1 Upper quarter (256 Kbits) Upper half (512 Kbits) All Protected Area M25P10-A none1 Upper quarter (512 Kbits) Upper half (1 Mbits) All M25P20
Note: 1. The device is ready to accept a Bulk Erase instruction if, and only if, both Block Protect (BP1, BP0) bits are 0.
Table 4. Protected Area Sizes (M25P40, M25P80, M25P16)
Status Register Content BP2 Bit 0 0 0 0 1 1 1 1 BP1 Bit 0 0 1 1 0 0 1 1 BP0 Bit 0 1 0 1 0 1 0 1 none1 Upper eighth (512 Kbits) Upper quarter (1 Mbits) Upper half (2 Mbits) All All All All M25P40 none1 Upper sixteenth (512 Kbits) Upper eighth (1 Mbits) Upper quarter (2 Mbits) Upper half (4 Mbits) All All All Protected Area M25P80 none1 Upper 32nd (512 Kbits) Upper sixteenth (1 Mbits) Upper eighth (2 Mbits) Upper quarter (4 Mbits) Upper half (8 Mbits) All All M25P16
Note: 1. The device is ready to accept a Bulk Erase instruction if, and only if, all Block Protect (BP2, BP1, BP0) bits are 0.
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AN1536 - APPLICATION NOTE
Consistent with its use on standard SPI EEPROM, the protection is started from the end of the memory. This means that, even if a given combination of Block Protect (BP) bits protects the same block size at the end of the memory, the address of the protected area is not the same across the different memory capacities of the devices. For example, (BP0, BP1, BP2) = (001) protects the upper 512 Kbits of the memory for the M25P40, M25P80 and M25P16, but not at the same address. Each device contains all the hardware necessary to conduct the complex Erase and Program algorithms internally, without further reference to the Bus Master. The duration of these algorithms is dependent on the amount of memory being addressed, which, in the case of a bulk erase algorithm, means that it depends on the memory capacity of the device, as summarized in Table 5. Table 5. Bulk Erase: Time to Erase the Whole Memory Area
Device M25P05-A M25P10-A M25P20 M25P40 M25P80 M25P16 Bulk Erase 512 Kbits 1 Mbits 2 Mbits 4 Mbits 8 Mbits 16 Mbits Duration of Erase Cycle 6 s (max) 6 s (max) 6 s (max) 10 s (max) 20 s (max) 40 s (max)
SPECIAL POINTS ABOUT THE M25P05-A Two final points should be noted, concerning the behavior of the M25P05-A that is distinctive: 1. The unused address bits (A23 to A16) are not Don't Care. They must each be set to 0 2. There is no roll-over at the end of the M25P05-A memory during a Read operation
CONCLUSION When designing an application to use an M25Pxx Serial Flash memory device, the application designer can allow for any member of the family to be substituted on the circuit board, because their footprints and pin-outs are the same. Thus one design can serve for a whole range of applications, from the lowest end of the range to the highest, provided that the few functional differences, noted in this document, are considered, and allowed for. To make this possible, the application software merely needs to act on the information contained in the Electronic Signature of the M25Pxx device.
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AN1536 - APPLICATION NOTE
For current information on ST Flash Memory products, please consult our pages on the world wide web: www.st.com/serialflash If you have any questions or suggestions concerning the matters raised in this document, please send them to the following electronic mail addresses:
apps.serial-flash@st.com ask.memory@st.com
(for application support) (for general enquiries)
Please remember to include your name, company, location, telephone number and fax number.
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is registered trademark of STMicroelectronics All other names are the property of their respective owners (c) 2002 STMicroelectronics - All Rights Reserved STMicroelectronics group of companies Australia - Brazil - Canada - China - Finland - France - Germany - Hong Kong India - Israel - Italy - Japan - Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States. www.st.com
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