Non Volatile RAM (F-RAM & NVSRAM) Forum Discussions
The nvSRAM has a specified tHRECALL (Power up RECALL duration) time for boot up / RECALL of data. When user powers up the device, at the end of the tHRECALL period, the device is ready for access. Which means user can perform read/writes. The tHRECALL completion is signaled at the HSB# (Hardware Store Busy) pin and user can start read/write based on HSB# going HIGH in case user is monitoring HSB# pin. HSB# will go HIGH in <= tHRECALL time. Since there is no restriction on what user can do after the part is ready, let us say user performs a write as soon as the part completes the power up RECALL and immediately powers down the part (planned on unplanned power down). The device will perform an AutoStore using the charge from the VCAP pin and it is guaranteed that the AutoStore will be successful under this condition also.
If user now has a capacitor on VCAP pin which is outside the spec, consider a 330uF which is higher than the datasheet spec limit of 180uF max, the capacitor would have charged to a lesser voltage than what would be the level if 180uF was on the pin. This would affect the AutoStore operation completion as described below.
During power down, when the VCC crosses VSWITCH, the power to the internal store circuit switches to the VCAP pin. From then on VCAP charge provides the power required to complete the AutoStore. Assume VSWITCH for the part is 2.4V and the store circuit needs to have a minimum voltage of 2.0V on VCAP to complete the STORE, then the capacitor value should be such that it accumulates enough charge on it to complete the AutoStore operation in tSTORE time (8 ms) while it discharges from 2.4 V to 2.0 V. In the case of higher capacitor, the starting voltage would be lower (since it was charged for the same tHRECALL time from the same internal charging circuit). However it still may accumulate sufficient charges to complete the AutoStore in time which is determined by the value of capacitor and its voltage level above 2V. On the worst case side, assume the capacitor did not even reach 2V because the capacitor value is too high. Then there will be a complete failure of AutoStore. Therefore, the higher value spec for VCAP is specified to guarantee that AutoStore will be successful if it is required to be done as soon as at the end of tHRECALL (= 20ms). If user still needs to use 330uF, user needs to ensure that AutoStore is not going to be required immediately after power up and ensure that there is sufficiently longer time before performing a write operation. (If there is no write operation after a NV operation, there will be no initiation of AutoStore since the NV data is same as the SRAM data). That is, give additional power up time before starting access, say add 20ms more before starting access.
Also note that the typical value mentioned in the datasheet is the minimum cap value with 10% tolerance which will ensure AutoStore will always be completed for any part across PVT (Process, Voltage, Temperature) range. And minimum value is the value net of tolerance (the minimum absolute value) which will ensure that AutoStore is successful across PVT. Please note that the performance of the part is the same if any value of capacitor across the min to max specification is used.
Show LessA nvSRAM memory cell integrates a fast access SRAM cell and a non volatile NV cell in a monolithic die. This cell structure offers the benefit of high performance SRAM access and non volatility of EEPROM/FLASH. In a typical system configuration where the system controller uses external memories for storing its firmware program and data, a Flash memory is used to store the program code and a SRAM is used to store runtime data and variables. During system boot up, the firmware code is first dumped into SRAM from the flash and then executes from SRAM.
S ince the nvSRAM combines SRAM and NV cells, it can potentially replace the combination of SRAM and FLASH with a single memory. After a power cycle, the data stored in NV cells of nvSRAM is available to SRAM after 20 ms (Power up Recall duration) which can be used by the controller for its boot up process. Once boot up process completes, the same SRAM space can be used as data memory for storing run time variables, parameters and scratch pad data. In this used model, the AutoStore feature of nvSRAM must be disabled so that SRAM data is never written back to its NV cell on its own by performing an AutoStore cycle. This will ensure that NV portion always stores the F/W program code. Disabling AutoStore features makes NV memory in nvSRAM as read only memory (ROM). To program the nvSRAM again with a new F/W code and store in its NV cell, on demand Software Store command can be issued which will Store a new code into its NV cell.
The only drawback with this approach is that data is not available in the SRAM for the first 20 ms during power up RECALL duration. It means controller boot up will start only after 20 ms. After 20 ms entire program memory is available in SRAM, whereas in SRAM+Flash combination, controller initially copies code from the program memory (Flash) to data memory (SRAM) on byte by byte basis.
Show LessHi All,
The new serial nvSRAM RTC devices can be used to detect less than a second using its newly added Square Wave generation feature. nvSRAM RTC devices can generate Square wave of frequencies 1 Hz, 512 Hz, 4096 Hz and 32768 Hz on INT pin. This along with RTC time keeping registers can be used to count less than a second.
Regards,
Harsha
Show LessHi,
We currently offer Asynchronous and Serial bus interfaces on our nvSRAM. What do you think are the most useful Synchronous interfaces for the future for our nonvolatile products?
Thanks
Ravi
Show LessThe datasheet for the CY14B256LA mentions 20-year data retention. Other nvSRAM products list 100 years. Is that 20 years from the most recent store operation, or 20 years total over the life of the chip?
Is there any way of reading the option status from the chip?
If AutoStore is disabled, does disabling it again count as a write as far as the life of the chip goes? For example, if the device containing the chip automatically disables AutoStore every time it turns on, does each disable operation contribute to "wearing out" the chip by eating into the 1,000,000 store count?
Does disabling AutoStore set the chip's "dirty bit" thus causing a store when /HSB is asserted?
If the dirty bit is set, are ALL bytes stored when /HSB is asserted, or only those bytes whose SRAM value differs from its stored value?
Thank you.
Show LessAs reference to AN45789 "Using Cypress nvSRAM as Program Memory"
Does that work to use cy14b256la as the one to cy7c68013a?
Or any other way that will be more suitable for cy7c68013a.
thanks
Allan Show Less
We have come up with a Junction temperature Calculator tool for all SRAMs for ease of use in calculating the Maximum Junction temperature in SRAMs.
I have attached zip file of the beta version of Junction temperature calculator tool below.
The Async tool will be applicable for NVSRAM and Asynchronous SRAMs. The Sync tool will be applicable for Synchronous SRAMs.
Do provide your comments.
Regards,
Pavan Show Less
Guys,
I recently figured out a nice thing about NVSRAM operation and thought it is worth sharing with everyone.
If NVSRAM is attempting AutoRecall and the power fails, AutoRecall will stop and next time the power comes back, previously stored (during AutoStore operation of course) data will be recalled. Similarly if power comes back during AutoStore operation, AutoStore operation will still be carried out and then AutoRecall will take place. In the end, it is not going to pose any problem in such corner cases....
cheers !
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