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A note about compact flash cardsSaturday, August 02. 2008A possible practical argument against using compact flash cards for memory buffers with Reprap machines... Recently, I've been thinking about moving over to the Mikroelectronika BASIC PIC development environment for Tommelise 2.0, not because it really needs the capabilities of this somewhat more expensive app, but rather because of some robotics work I have planned for next year which will require the use of at least Pic 24F controllers. While thumbing through their very detailed users' manual I noticed something that might bear on an extended discussion that we have been having about the relative merits of various ways of appending print buffers and off-line printing capability to our various approaches to controlling Reprap machines. Compact flash cards have been a much discussed candidate for this role. When I discovered that Mikroelectronika had a library for handling this sort of device, I was naturally interested. My interest was rather lessened when I got a look at their sample schematic.  The long and short of it is that it appears that to implement such a storage device you are going to require two full ports. For a 40 pin PDIP controller chip that is a LOT and leaves you precious little left to actually control your Reprap machine. Just in passing, Mikroelektronika has what more or less amounts to a Visual Studio situation for microcontroller programming, that is, they have identical compilers in BASIC, Pascal or C depending on your taste in computing languages. BASIC is the cheapest at $149 while C, of course, is the most expensive at $249. They also carry a huge selection of premade development boards the variety of which reminds me more than a little of Arduino. Interestingly as well, they offer boards and, I think, compilers for the ARM chip. As long as NATO doesn't decide to bomb Serbia again, I think they will be a reliable supplier. Trackbacks
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For some reason flash card interfaces wildly vary in the number of pins they require. There's definitely one which requires very few (if used in a low pin count mode). I think it's SD, but I can't quite remember.
Alex is right, the SD card uses a 4-wire SPI interface.
To increase I/O ports, I like to chain uCs together. So for the CF card, you could set one uC to take parallel data/commands in on 8-10 wires, or serially with i2c or spi, and have another uC do the actual work. Basically, one uC would simply run the CF card, and the other would do the rest of the work.
This adds a uC for the CF card interface, but it could be a smaller, slower uC because it only needs to be fast enough to run the CF card and need 18 pins for the CF plus 2-10 pins for communication.
SD cards have data in, data out, clock, and chip select lines. Four pins for the uC, max. Then there's a couple ground lines and a 3.3V power line. There is a protocol in there using SPI specifically for microcontrollers to use.
CF cards are absolutely not what we've been talking about. I'm guessing that's a parallel interface rather than a serial one like SD ;)
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