How to test memory in an HP48 RAM card

[Jonathan Busby]

(01-25-2021 12:15 AM)mfleming Wrote:  

(01-24-2021 07:04 PM)Jonathan Busby Wrote:  If the Cypress F-RAM chip had a, say, 192MHz clock instead of just 40MHz, then there'd be no problem. I've been in correspondence with a Cypress Semiconductor engineer, so we might find out if Cypress Semi is planning on releasing faster chips any time soon.

I've looked at a number of persistent memories and the fastest clock I can remember seeing was 66 MHz. See what's available in quad-SPI memory. With a higher clock rate that might get you in range, though I know of no low end microcontroller with hardware QSPI support.

Cypress Semi makes F-RAM chips that have 100 trillion ( as opposed to 1000 trillion in their device which I really want to use but may be too slow ) read / write cycles and clock speeds of 108MHz for SDR QSPI and 54MHz for DDR QSPI. The downside is that the read / write endurance is less than a factor of ten than the chip I really want to use. Also, the power consumption is higher and the highest capacity chip is only 4Mbit x8 . I guess I *could* use this if I implemented a "flash translation layer" in hardware using a low power CPLD or FPGA. I know that F-RAM isn't flash but since both wear out, the same principles and algorithms used for wear leveling in NAND flash would mostly also apply to F-RAM. I just wish that their 1000 trillion read / write endurance part was faster or supported QSPI :/ It would make things a lot easier.

Regards,

Jonathan

[mfleming]

How about this M-RAM chip from Renesas?
https://www.mouser.com/ProductDetail/Ren...Gi8g%3D%3D

QSPI @ 108 MHz max, single and double data rate, 10^16 write cycles, 20 year data retention, 4/8/16 MB in 8 pin package. About $19 bucks in single qty.

BTW, the typical three score & ten human lifetime is about 2.2e9 seconds, so 100 or 1000 trillion cycles is probably overkill for most applications, especially handheld calculators

[Jonathan Busby]

(01-27-2021 07:44 PM)mfleming Wrote:  How about this M-RAM chip from Renesas?
https://www.mouser.com/ProductDetail/Ren...Gi8g%3D%3D

QSPI @ 108 MHz max, single and double data rate, 10^16 write cycles, 20 year data retention, 4/8/16 MB in 8 pin package. About $19 bucks in single qty.

BTW, the typical three score & ten human lifetime is about 2.2e9 seconds, so 100 or 1000 trillion cycles is probably overkill for most applications, especially handheld calculators

Thanks for the tip! That's a really nice chip!

The reason I hadn't considered MRAM is because all the devices I had investigated ( up until now ) either had too high operating currents or had a huge startup current. The one to which you linked has a maximum write current of 30mA, which is quite high on the HP48GX, but, I think it's not a problem.

The chip also can run in QSPI XIP 54MHz DDR mode, which is excellent. Also, the write endurance is even higher than the Cypress Semiconductor chip I was considering which was about 1000 trillion cycle -- this MRAM chip is 10 orders of a magnitude more durable with \(10^{16}\) write cycles!

After more research, I think I may instead go with the MRAM chip to which you linked instead of F-RAM.

Thanks!

Jonathan

[mfleming]

(01-27-2021 09:39 PM)Jonathan Busby Wrote:  The reason I hadn't considered MRAM is because all the devices I had investigated ( up until now ) either had too high operating currents or had a huge startup current. The one to which you linked has a maximum write current of 30mA, which is quite high on the HP48GX, but, I think it's not a problem.

The chip will spend a significant part of its time in the quiescent state (10 uA) even when the 48 is using it, so average power consumption won't be bad. Have a nice reservoir cap across its rails, and put me on the order list