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Old Jun 12, 2003, 1:25 AM   #11
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It does appear that SD (SEcure Digital) is becoming more prevalent, in many devices, including digicams, and even canon have a model out now.

I don't think the SD's smaller form factor is going to be much of a limiting factor.
256Mb is pretty common, There's even mini SD emerging, in an even smaller form factor. Sony's Mem stick proves you can squeeze 1Gb plus a controller, into something around that size.

Doesn't it make for sense to put the controller in the camera, not on the flash card. Then the camera can have more optimised power management.. And also the flash memory end up cheaper, as there's less replication.
SD is pretty fast, and there's SDio to,
Plus there's all the hastle for users, in deciding the flash speed to buy, and inventory/stock issues for dealers and manufacturers, which just complicates matters, and keeps the cost higher.

it would seem that SD isdefinitely worth considering.
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Old Jun 12, 2003, 6:24 AM   #12
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I believe we touched on this issue before (complete pinouts of SM and sD/MMC):

While I agree with Vox than faning out the flash NAND cells to the I/O pads is kind of logical. The only problem with this approach is, the low-level driver is now with the camera firmware, and as flash technologies improve so too must the camera's firmware. The manufacturers rather work on outputing new gears than improving old ones (beside fixing bugs), hence the other reason for the demise of Smartmedia. Many former Olympus owners have found this out when they can't just simply use higher density cards in their cameras (some cards even change voltages as well). My Agfa 1680 is another perfect example... before the time where everyone settle for this 128M max... :twisted:

With a standard interface like on the newer flash cards and particularly the IDE interface which is standardized by the CF association, the camera firmware just treat this I/O as a standard hardisk. Serial interface like the MemoryStick or MMC has it's benefit too since it could be spec'ed like a "USB/Firewire" or "SATA".

May be our resident flash drivers 'expert" Eric S (I'm just a H/W guy) can help me out here, but all bare flash memory cells, be it NAND or NOR required a different drivers with different cycles and timings especially in the write sequences. I'm familiar with Intel and AMD (ie NOR structure), and rarely do they come out with new chips with the driver compatible with the old ones (even though they all have the same pin-out). Reads are never a problem since the NOR cells are just like any ROM, but writes required different algorithms... ops: ops: ops:

To top this off, NAND cells which are used by memory cards are accessed serially very much like a hardisk even though they have multiple I/Os parallel pads, ie the address/command are sent 1st then follow by block of data bytes... plus remember there's all this logical to physical address translation and memory management stuffs as well! Beside all flash cells have limited write cycles hence the drivers have to keep a rolling count as to not just overwrite the same location too many times or there goes your flash! :lol:

The controller in the card is a good thing after all. All new cards have them, not that it also helps to ensure the manufacturers from being sued either since they can also incorporated the "serial copy management" scheme for copyright music but also another reason contributing to the quiet death of Smartmedia...
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Old Jun 12, 2003, 9:28 AM   #13
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To add what I know/remember.

Background. Flash are broken up into chunks (blocks?) based on an addres line. So 32K blocks, or 16K blocks, for example (Probably larger now.) When yo uwrite to them, you have set the block into a "Write state". You do that by writing a certain pattern of bits to the flash which tell is that you want a write state and which block it should set. Then you write the data to each address in that block. (I think there is also a way to verify that the write worked, besides reading the data again, but I don't remember... It has been a while.)

Problems. So different flash chips can have different size blocks and different patterns to enable, disable, & verify. Many times, the chips will be compatable because this is a selling point "upgrade hardware designs which you flash model XX-YYYYY, and you get double the memory without changing your hardware design!" If you can keep the software exactly the same, then you're in luck. But it is possible that they'll change the write pattern.

And you are also right that that timings and tollerances can be different. I bet that has more to do with what clock the memory can use (i.e. accept data faster, have tighter timings.) But I'm sure that changes as well.

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