Joined: Fri Aug 30, 2002 1:09 am
Posts: 8538
Location: Southern California
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We had a tape modem topic at viewtopic.php?f=4&t=82&p=463#p463 14 years ago. I can probably find the schematic of the tape modem I designed for work in the 80's which used kind of a lot of parts but all of them together came to a dollar or less. I'll need some time to find it and clean it up and make it presentable. It looks like I was using the Kansas City standard that Ed referenced, although I didn't know it at the time. Experimentation led me to come up with it, not knowing I was re-inventing the same thing.
I've frequently read that tape playback level was pretty critical on many systems. On mine, it didn't matter, because I used a huge amount of gain to get it up to clipping anyway to turn it into a square wave. It was very reliable, and I never had an error at 300bps. Gong twice as fast, 600bps, there would be a wrong bit every few K. If you can modify your tape transport to move the tape faster, you could safely get the data rate much higher, two, four, or maybe even eight times as fast (subject to head limitations and tape handling ability).
At this point though, if you can implement I²C for serial EEPROMs or SPI for flash (basically by adding a 65c22 VIA to your board, you can get away with
- lower cost
- faster speeds
- smaller size
- better reliability
- essentially random access (compared to tape which has to be wound)
all at once. The 65c22 VIA will give you a lot of I/O bits left over for other things too since the I²C or SPI won't need nearly all of them, and you'll get timers and other benefits as well.
As much as I like tape recorders, I have to say they're no longer a viable data storage method, especially when you consider the fact that they use rubber belts that rot over time and replacements are no longer available. [Edit, years later: I find that there are places that still sell them online. I don't know if they're being made, or if it's old stock. One place is here.] When I worked at TEAC, we would always replace the rubber parts (belts, idlers, pinch roller) when a tape recorder came in for repair, regardless of what it was there for, to extend the life concerning those parts, since we'd have the machine open anyway.
I and Daryl (8BIT) have used I²C EEPROM modules made to the I2C-6 connector standard. Mine look like this:
Attachment:
EEPROMmodule.jpg [ 10.59 KiB | Viewed 366 times ]
You can see the 8-pin DIP under the translucent heat-shrink. These top out at 32KB for simple addressing, and, I believe, 128KB for addressing them as four 32K's in one IC.
More recently, I've used our SPI-10 hobbyist-friendly connector standard and I have the tiny PCBs for these flash modules shown on the front page of my site available to supply to others. If you just want a few, the cost is hardly more than just the postage. They're about half the area of an SD card, but the flash memory that goes on them (I'm using 4MB ones in SO-8) is much simpler to interface to in terms of your software. Here's a picture, comparing them to the size of SD card and Compact Flash:
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25VFrevBcompare.jpg [ 63.89 KiB | Viewed 366 times ]
The one slight drawback about the flash modules though, unlike the I²C ones, is that they require 3.3V, so you'll probably have to do voltage translation, which is easy to do since there are only four signal lines and none of them are bi-directional. (You'll need a fleapower 3.3 power supply of some sort too. I've use an LM317LZ in a TO-92 case.)
_________________ http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?
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