First CPU project, oscilloscope and more

[BigDumbDinosaur]

GARTHWILSON wrote:

Errr... make that "logic probe." Here's a logic analyzer, the Agilent 16821A 34-Channel Portable Logic Analyzer, kind of a low-end one, at $26,000 starting price:

What a bargain! I'll take two.

[BigDumbDinosaur]

Goerofmuns wrote:

Quote:

Here's a logic analyzer, the Agilent 16821A 34-Channel Portable Logic Analyzer, kind of a low-end one, at $26,000 starting price:

AgilentLogicAnalyzer.jpg

Oops. I meant logic probe, thanks.

Avoid the temptation to buy one from eBay, as many are inferior counterfeits (my grandson bought one and I can tell you it is a piece of junk). Mouser sells the genuine BK Precision DP-21. The current model is the descendent of the (beige) one that I purchased in 1989 and still use.

[Goerofmuns]

http://uk.mouser.com/Search/ProductDeta ... y615-DP-21

This one? Got it on my basket.

[BigDumbDinosaur]

Goerofmuns wrote:

http://uk.mouser.com/Search/ProductDetail.aspx?R=DP_21virtualkey61500000virtualkey615-DP-21

This one? Got it on my basket.

That's the animal. A friend of mine bought one a few years ago and had me replace the power lead alligator clips with the spring-and-hook type. Otherwise, he's quite satisfied with it.

[Goerofmuns]

Ok, so how's this memory? Everything *seems* to check out, I may be making a big noob mistake though.

[GARTHWILSON]

Goerofmuns wrote:

Ok, so how's this memory? Everything *seems* to check out, I may be making a big noob mistake though.

I'm not sure I've heard of the brand, but the "6264" part of the number says it's a pretty standard 8Kx8 SRAM that's easy to use.

[BigEd]

Should be fine, but this 32k x 8 one is a bit faster and not much more expensive:
http://uk.mouser.com/ProductDetail/Alli ... MCR2WtI%3d

[Goerofmuns]

Wow, again what a great forum. I've been on forums where people would have been complaining about me posting so much, it's really encouraging! Looks good on the faster memory, my favorite thing about this sort of stuff is that components are so cheap. So now we have ROM, ROM programmer and of course wires etc...

I don't want to bother with IO yet, I want bare-bones. I know I'm not going to make a full featured computer after a couple weeks of reading.

[BigEd]

Very glad you like it here! BTW, when the topic has drifted away from the original description, please start a new thread with a new description.

(Many of us use these forums both as a place for conversations and as a searchable reference)

If there already exists a similar conversation, even if it is years old, feel free to continue it - you'll often find that the original participants are still active, and of course it means we get one thread instead of two for future searches.

Cheers
Ed

[BigDumbDinosaur]

Goerofmuns wrote:

Ok, so how's this memory? Everything *seems* to check out, I may be making a big noob mistake though.

I read the data sheet and it seems to be pretty conventional SRAM, as Garth notes. However, it's only 8KB and at 70ns, is kind of slow. Perhaps this product may be better for your application. It has a slightly simpler control interface (/CS, /OE and /WE), gives you four times the storage of the other part for only a little more cost, and is much faster at 20ns.

If you are willing to work with SMT packages, you can get 10ns 5 volt SRAM up to 512 KB. Dunno your application, though.

[Dr Jefyll]

Goerofmuns wrote:

I want bare-bones.

In that case, there's a minor downside to Ed's and BDD's well-meaning advice. It's true the RAMs they suggest are larger and faster, but those chips lack the extra chip-select input found on your Alliance device. In a bare-bones design that extra (active-high) chip-select input is likely to come in handy, eliminating some of the glue logic -- saving a NAND section and/or an inverter section. (I did say "minor," didn't I? )

In the long term you'll probably want a bigger, faster RAM, but the Alliance part may be worthwhile if you don't mind buying something for the short term.

-- Jeff

[BigEd]

Very good point about the multiple chip selects - thanks!

[GARTHWILSON]

Goerofmuns wrote:

I don't want to bother with IO yet, I want bare-bones.

Well, a computer with no I/O is pretty worthless, in fact, pretty safe as you'll never detect any bugs. Again you can go back to the 6502 primer though, and the first diagram on the "circuit potpourri" page is of a whole, basic computer, with a single 65c22 VIA for I/O, and the address-decoding logic leaves room for lots more I/O ICs if you want to add them later. Following that diagram, there are many ways to use the VIA for probably a lot more things than you thought possible-- even lots simultaneously. (I have more coming, when time allows.)

BigEd wrote:

If there already exists a similar conversation, even if it is years old, feel free to continue it - you'll often find that the original participants are still active, and of course it means we get one thread instead of two for future searches.

Yes. Please. Some people on other forums think that if it's old, they should start a new topic-- and then they just end up cluttering the forum with repeated material.

[BigDumbDinosaur]

Dr Jefyll wrote:

Goerofmuns wrote:

I want bare-bones.

In that case, there's a minor downside to Ed's and BDD's well-meaning advice. It's true the RAMs they suggest are larger and faster, but those chips lack the extra chip-select input found on your Alliance device. In a bare-bones design that extra (active-high) chip-select input is likely to come in handy, eliminating some of the glue logic -- saving a NAND section and/or an inverter section. (I did say "minor," didn't I? )

In the long term you'll probably want a bigger, faster RAM, but the Alliance part may be worthwhile if you don't mind buying something for the short term.

-- Jeff

Good point, Doctor!

[Dr Jefyll]

Garth makes a good point, too -- about a computer with no I/O being free of (perceptible) bugs!

Seriously, though, there's a lot that can be learned with just a logic probe or 'scope, especially if you can slow the CPU clock down to almost zero. So bare bones is OK. You don't need a UART or VIA; for starters you can let the 'scope or logic probe be your output device.

Edit: BTW, that extra chip-select input seems to be standard for 6264-type rams. (I guess I used to know that, but it's been a long time since these parts were current & noteworthy!) Anyway, Alliance isn't your only option. You'll probably find all the 6264's have that extra chip-select.

-- Jeff