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[BigDumbDinosaur]

GARTHWILSON wrote:

In ye olden days, the Φ2 output always went to the other things that took Φ2...

That was back when clock generators were too weak in the knees to run more than one or two TTL loads. Clock generators have greatly improved, and in modern systems, everything is CMOS.

[BigDumbDinosaur]

allisonlastname wrote:

This better?

Yep! You’ve got the resistor in the right place.

[barnacle]

allisonlastname wrote:

All the 74 is supposed to be 74HC but kicad only has 74LS symbols for a lot of stuff.

Double click on the part name on the schematic to change it, once you've selected the logic symbol. Your BOM will be correct then, too.

Neil

[allisonlastname]

I've run into an issue. Mouser don't have any 28c256, 28c64 or 28c010 chips in stock, and they won't have any until mid-july.

What can I use instead of those?

[Sean]

allisonlastname wrote:

I've run into an issue. Mouser don't have any 28c256, 28c64 or 28c010 chips in stock, and they won't have any until mid-july.

What can I use instead of those?

Jameco still has the 28c256 in stock:
https://www.jameco.com/z/28C256-25-Majo ... 74878.html

[floobydust]

allisonlastname wrote:

I've run into an issue. Mouser don't have any 28c256, 28c64 or 28c010 chips in stock, and they won't have any until mid-july.

What can I use instead of those?

How soon are you looking to obtain parts? I'm going to start selling off my 5-volt inventory of parts... much stuff, including AT28C256 in 28-pin DIP and 32-pin PLCC, AT28V64 in DIP... lots of 74HC/HCT logic chips and the list goes on.... note that I'm moving over to SMT and 3.3-volt stuff... and away from pin-in-hole designs.

[allisonlastname]

Sean wrote:

Jameco still has the 28c256 in stock:

Ordering from Jameco would appear to mean transatlantic shipping, which is generally undesirable, not least for reasons of time.

floobydust wrote:

How soon are you looking to obtain parts?

Pretty soon. See note above about transatlantic shipping.

I did notice that someone else earlier in the thread suggested a 39SF010, which I'm not entirely sure about due to it being flash and not EEPROM. My thought is that it might be harder to program, but I could be completely wrong.

[floobydust]

Not sure of your location.... so shipping would be what it is.... as I'm based in South Florida.

The flash devices have a different programming structure. My Monitor code can program the AT28C256 insitu for single/multiple bytes. The flash devices are sector based... from the datasheet, you need an unlock sequence first, then an erase of a 4KB sector, followed by programming the sector with the new data. Certainly different, but shouldn't be a problem. One thing to note however... the unlock sequence is done by sending specific byte patterns to specific addresses first. The spread on those addresses is around 24KB or so... so if you're not accessing that much of the chip, programming it insitu is not an option. I found the same issue with the Atmel AT28BC256 (battery voltage 3.3v EEPROM). I changed the memory addressing so only 8KB of EEPROM is accessed and I can't use my Monitor code to change it... drats!

[drogon]

allisonlastname wrote:

Sean wrote:

Jameco still has the 28c256 in stock:

Ordering from Jameco would appear to mean transatlantic shipping, which is generally undesirable, not least for reasons of time.

Mouser has it in the UK (which is where I think you are)

https://www.mouser.co.uk/ProductDetail/ ... grbg%3D%3D

However at that price, I suspect an alternative would be better.

Quote:

Pretty soon. See note above about transatlantic shipping.

The issue for us in the UK right now is not just time, but import duty, VAT and local postage. It can double the cost of some things if not careful.

-Gordon

[BigDumbDinosaur]

Sean wrote:

Jameco still has the 28c256 in stock:
https://www.jameco.com/z/28C256-25-Majo ... 74878.html

That is a very slow part, 200ns.

[Paganini]

UTSOURCE has fast ones for ~$5.

https://www.utsource.net/itm/p/6175055.html

They are pulls, but I bought some and they seem to be high quality.

[No True Scotsman]

allisonlastname wrote:

I'm planning to build it on a breadboard to save having to design a PCB or learn wire wrap....

Have you considered these stripboards that have the traces laid out like a breadboard?

https://www.ebay.com/itm/114721914362

They come in various sizes. This is just the example that came to hand the quickest. Some are big enough for several rows of ICs. I like the ones like this one where the ICs straddle both power rails. It makes it easy to connect VCC and ground, and place a capacitor near each chip.

[No True Scotsman]

No True Scotsman wrote:

They come in various sizes.

Here's one with two rows.

https://www.ebay.com/itm/115271688771

The "5er" in the description refers to the fact that there are 5 pinholes at each connection point. You'll want to base your purchase on how many jumper wires will be connected to each IC pin. Bear in mind that wide DIPs will obscure some of the holes, but you can usually snake a couple of 22 AWG wires under a chip and solder them on before you solder the chip.

[allisonlastname]

Slight issue:

2023-08-16_22-54.png (10.12 KiB) Viewed 7228 times

But yes, I have seen those boards before and they look useful.

[GARTHWILSON]

No True Scotsman wrote:

No True Scotsman wrote:

They come in various sizes.

Here's one with two rows.

https://www.ebay.com/itm/115271688771

That one has two rows down the middle of the ICs also, which for better for getting good power and ground connections between ICs, since you don't have to go clear out to the sides which increases the inductance.  I also solder the bypass capacitors across these two rows, underneath the ICs, which gives much lower inductance.

Quote:

The "5er" in the description refers to the fact that there are 5 pinholes at each connection point. You'll want to base your purchase on how many jumper wires will be connected to each IC pin. Bear in mind that wide DIPs will obscure some of the holes, but you can usually snake a couple of 22 AWG wires under a chip and solder them on before you solder the chip.

These solder-type breadboards allow you to get more than one wire or lead per hole, so in that sense they're more versatile than the solderless ones.