I have a question regarding the RH850 Flash number of rewrites:
Based on the RH850/F1KH, RH850/F1KM datasheet page 222 (3A.7.2) where I see the following sentence:
Note 1. The number of rewrites is the number of erasures for each block. When the number of rewrites is “n” (n = 125000), the device can be erased “n” times for each block. For example, when a block of 64 bytes is erased after 4 bytes of writing have been performed for different addresses 16 times, the number of rewrites is counted as 1. However, multiple writing to the same address is not possible with 1 erasure (overwriting prohibited).
Please could you clarify the followings:
1. When in the sentence is saying 4 bytes of writing in a block of 64 bytes means in 16 different address meaning 4 bytes per address it means I am writing 1 time 64 bytes or 16 times?
2. What about the erase after 4 bytes what that means ? After write a 4 bytes address I should erase once ?
Another question is retention policy of 250K number of rewrites in 3 years what that means ?
I really need to clarify as its' not clear what is the strategy to count as 1 write in the flash.
Thanks a lot,
Essentially what this explanation is trying to say is, the data-flash memory is erased in 64-byte blocks, a write to any 4-byte (1-word) address in this block (of which 4-bytes is the minimum write size) followed by an erase counts as one (1) write / erase cycle.
The data-flash is designed to retain for 20yrs for the first 125K write / erase cycles. After 125K, the guarantee is 3yrs, up to 250K write / erase cycles.
A good EEPROM emulation strategy will wear-level the data, i.e. spread out the writes across multiple addresses.
If your application is non-AUTOSAR / non-FuSa (i.e. QM), you can use the RH850 EEPROM emulation library (EEL) with the corresponding FDL. For AUTOSAR and/or FuSa applications the recommendation would be to use the low-level MCAL driver (FLS) along with a 3rd party FEE. Unfortunately Renesas does not offer the FEE module for RH850 devices.
RV28F / RV40F DataFlash Usage
RH850 - Data Flash Library (FDL) Manual - Software
RH850 - Data Flash Library (FDL) - Software
I would have pointed you to the European MyPages portal for the EEL but I understand this is going away in a few short weeks. I don't know the alternative / new method of obtaining such a software package and documentation.
Thanks for the answers:
One more clarification please in case we are planning to use 250k in 10 years would that meaning a different behavior as the spec says 125k in 20 years ?
Another confirmation is that Note 2 states the following:
Note 2. Retention period under average Ta = 85°C. This is the period starting on completion of a successful erasure of the data flash memory.
Is this means the test was done over the average temperature of 85C ?
I'm not sure if your first question directly relates to the memory retention characteristic. If the life of the product is expected to be only 10yrs, and the expected number of rewrites of a flash block is 250K over this time lifetime, this is a different specification.
Understand that after 125K cycles, the memory contents are valid from 3yrs after the erase of the block was performed as the 250K retention specification applies.
Higher temperatures can impact data retention, so yes if avg temp exceeds 85C then the guarantee of the specification is no longer valid.
Hello JimIts mentioned that data is erased in sets of 64bytes and a 4bytes write is sufficient to be considered as a memory erase cycle
1) how many set of 64 bytes is considered as a page erase? Does this part have a concept of page erase?
There is no page erase, only a block erase of 64-bytes.