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Garth Wilson · 05-10-2016, 01:04 AM

(05-10-2016 12:03 AM)Sylvain Cote Wrote:
(05-09-2016 11:19 PM)Garth Wilson Wrote:

it would be nice to have a module with more flash, or that accommodates microSD cards or something like that;

That will have to be seen ...
Assuming we have something like a pageable HePaX memory module of 16KWord per page (= 32KB/Page non-optimized)
and we take a small (by today standard) 32 GB SD memory card then we have a system with 1 Mega pages to manage!

I'm thinking more in terms of file storage, to have an onboard replacement the HPIL microcassette drive or floppy-disc drive. It looks like the densest available in SO-8 is Microchip's SST25VF064 at 8MB. The Spansion S25FL512S has 64MB in an SO-16. They have 2-die one in that size for 128MB. MicroSD's density is so high there would be no risk of ever using even 1% of it, but it would be removable.

Quote:
(05-09-2016 11:19 PM)Garth Wilson Wrote:

and perhaps an SPI or I²C port and the drivers could be put in a module.

+1
With only two wires (not counting VDDs), I think I²C is better adapted to the HP-41 than the SPI who need a slave select (SS) for each peripheral on the bus.

At first I was thinking of the wasted power of I²C's passive pull-ups (since the 41's batteries are so small), but then realized they could be external. The 41's speed would not give any risk of being held up by I²C's speed, so speed is not a reason to favor SPI. However, some things are available in SPI and not I²C, like the denser serial non-volatile memories discussed above. I²C EEPROM only goes up to 128kB IIRC, and you have to address it like four 32kB ones IIRC. Finally, I²C would allow a tiny 3-conductor (including ground) 2.5mm phone plug. The 1-Wire interface would be even more suitable in that regard, but less suitable in other respects. I think 1-Wire goes too far. I do like I²C and SPI and have used them a lot.