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Johnny Starr
PostPosted: Tue Aug 06, 2013 6:18 pm 
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Hello again.

I'm about to embark on a few projects, and I want to have the right parts for the jobs. I'm going to be working on several microproc projects: 6502, z80, 6809, and whatever else I get my hands on. I'm a bit ignorant when it comes to memory though.

For instance, I've seen a lot of EPROMs out there and EEPROMS. I know the difference, but what I'm not certain about is compatibility. Do I just need to search for CMOS compatible memory?

I also don't understand the programmers out there. Ebay ranges in price from as little $11.99 for an EEPROM programmer, all the way up to $200.00

I don't want to get stuck collecting the wrong memory for the job. I am hoping for a list, or some other comprehensive resources that I can refer to when shopping.

BTW, am I overthinking it? Will I be ok with just about anything out there?

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Aslak3
PostPosted: Tue Aug 06, 2013 8:03 pm 
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Hi there,

Wowsers, 3 different CPUs. Have fun. :)

EEPROM is the easiest to handle in my experience. Something like the http://www.atmel.com/Images/doc0006.pdf 28C256. Readable as a SRAM, and writeable with standard TTL voltages. As far as programming it goes, I made my own for the same reasons you've found (cost). Home made EEPROM programmers are being discussed on another thread around here. Of course an off the shelf programmer will work nicely enough. Just look for one within budget, supporting your OS of choice, and the EEPROM you want to use.

Lawrence

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Last edited by Aslak3 on Tue Aug 06, 2013 9:11 pm, edited 1 time in total.

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GARTHWILSON
PostPosted: Tue Aug 06, 2013 8:26 pm 
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Aslak3 wrote:
Home made EEPROM programmers are being discussed on another thread around here.

at viewtopic.php?f=4&t=2491

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nyef
PostPosted: Tue Aug 06, 2013 9:44 pm 
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You might also consider something like the SST 39SF010, 020, and 040 parts, available in DIP and other form factors. 5v programming and operation voltage, in-system programmable (though you'll need to run your programming code from RAM or from a different ROM, as the ROM itself can't be used for normal operation wihle programming). Your problem then becomes that the smallest ROM is 128k, which is larger than your typical 8-bit address space.

When I was working with embedded 6502-derivative and Z180 systems we were using the Atmel AT49F and AT49LV parts, and later the AMD Am29F and Am29LV parts, but I didn't do the hardware design on those systems, so I'm not sure quite how easy they are to interface. I can't imagine that they'd be too hard, though.
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GARTHWILSON
PostPosted: Tue Aug 06, 2013 9:52 pm 
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Your problem then becomes that the smallest ROM is 128k, which is larger than your typical 8-bit address space.

not really a problem, as there's no obligation to use the whole thing— you could tie the two high address bits high or low for example to get 32Kx8.

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Johnny Starr
PostPosted: Tue Aug 06, 2013 10:01 pm 
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GARTHWILSON wrote:
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Your problem then becomes that the smallest ROM is 128k, which is larger than your typical 8-bit address space.

not really a problem, as there's no obligation to use the whole thing-- you could tie the two high address bits high or low for example to get 32Kx8.


What does 32Kx8 really mean? Its a total of 32K right? Does the 8 mean that it outputs 8 bits? Are there 32Kx4 or 32Kx16?

Are there any forms of memory that aren't compatible with CMOS that come in 32Kx8?

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nyef
PostPosted: Tue Aug 06, 2013 10:04 pm 
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True, or attach a '174 or similar to one of your VIA outputs to supply high bits for the ROM address (the '174 has a reset line as well, allowing the system to start up in a known state). Or you could burn some address space and have the latch inputs wired directly to the CPU data bus.
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whartung
PostPosted: Tue Aug 06, 2013 10:13 pm 
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Johnny Starr wrote:
What does 32Kx8 really mean? Its a total of 32K right? Does the 8 mean that it outputs 8 bits?


32K x 8 bits

Back in the day, you might get a 16K RAM chip, but it's 16K x 1, meaning it's 16K BITS, and you would need 8 of them for 16K BYTEs.

By the same notion, you might find a 1K RAM that was 256 x 4, that is 256 4 bit words, and would need 2 of them for 256 bytes of RAM.

So, you have to be careful when looking at memory descriptions, you can't go by simply "32K" alone, it's important to find out "32K of what".
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nyef
PostPosted: Tue Aug 06, 2013 10:22 pm 
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The flipside to the 16Kx1 DRAMs is that you'd also see them used in sets of at least nine, so that you had a parity bit, or more so that you had a bit or two of ECC.

Actually, some 30-pin SIMMs had a couple of 1Mx4 DRAMs for the main memory and a 1Mx1 DRAM for parity. Same principle, really.
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BigDumbDinosaur
PostPosted: Tue Aug 06, 2013 10:54 pm 
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Johnny Starr wrote:
I'm a bit ignorant when it comes to memory though.

For instance, I've seen a lot of EPROMs out there and EEPROMS. I know the difference, but what I'm not certain about is compatibility. Do I just need to search for CMOS compatible memory?

By "memory," are you referring to volatile random access memory (RAM, usually static RAM for 65xx/68xx projects) or something that permanently retains data when the system is dead? You could, of course, use certain EEPROMs as RAM, as long as they can be read and written like RAM.

If your goal is to have non-volatile RAM, consider that modern asynchronous static RAM (SRAM) can be battery-backed and when not being accessed, draws microamperes, which means the data can be retained for very long periods of time (years, in fact). When your system is powered, you would supply power to the SRAM in place of the battery output, which means the battery isn't being used at all during regular operation.

If your storage doesn't have to be writable during normal system usage, either a JEDEC standard EPROM or EEPROM is suitable. I use the 27C256 EPROM in my POC unit, which is a 32K x 8 device. They are available down to 55ns (see Jameco P/N 266079), 45ns in OTP (one-time programmable) configuration, which is essentially like the old fashioned PROMs we used back in the 1970s.

Quote:
I also don't understand the programmers out there. Ebay ranges in price from as little $11.99 for an EEPROM programmer, all the way up to $200.00

As always, you only get what you pay for. The more expensive programmers are usually much higher quality and support more devices. I purchased a 55 dollar unit from eBay about 5 years ago and ended up having to replace the ZIF socket because it wore out after less than a year's worth of use. The software that came with it was pretty bad as well.

Quote:
BTW, am I overthinking it? Will I be ok with just about anything out there?

I don't think you're overthinking. You're being prudent with finite resources: your time and money.

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GARTHWILSON
PostPosted: Tue Aug 06, 2013 11:08 pm 
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Quote:
If your goal is to have non-volatile RAM, consider that modern asynchronous static RAM (SRAM) can be battery-backed and when not being accessed, draws microamperes, which means the data can be retained for very long periods of time (years, in fact).

The first CMOS 6502 comuter I made was in the 1980's and was a prototype for something that was later to go into production. I had a 10µF capacitor across the SRAM's power, but the SRAM keep-alive circuit was not active yet, and I found by accident that when I came into work in the morning, the 10µF capacitor had prevented the SRAM from losing its memory overnight in the absence of power. That would put the leakage at least down into the picoamp range! Impressive.

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BigDumbDinosaur
PostPosted: Wed Aug 07, 2013 12:18 am 
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GARTHWILSON wrote:
Quote:
If your goal is to have non-volatile RAM, consider that modern asynchronous static RAM (SRAM) can be battery-backed and when not being accessed, draws microamperes, which means the data can be retained for very long periods of time (years, in fact).

The first CMOS 6502 comuter I made was in the 1980's and was a prototype for something that was later to go into production. I had a 10µF capacitor across the SRAM's power, but the SRAM keep-alive circuit was not active yet, and I found by accident that when I came into work in the morning, the 10µF capacitor had prevented the SRAM from losing its memory overnight in the absence of power. That would put the leakage at least down into the picoamp range! Impressive.

Also to note is that most of the available SRAM can be operated at pretty low voltages, making a CR2032 3.3 volt battery sufficient to maintain RAM contents. For example, the CY7C1049D SRAM that Garth uses in his 4MB DIMM will maintain data down to 2 volts.

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