8-bit CPU: Ordering the parts

In order to start building, I need some materials and parts, I have to order those first.

In terms of logic chips I decided to go with 74HC* series (Ben used 74LS* in his builds). Why? Well, it looks like it's newer design with lower power consumption, also the list of what's currently is stock looks better. I won't be able to mix the logic families trough, there are some differences on what voltages are considered LOW and HIGH between them.

I decided that for start I could try to build:
  • Clock module
  • Register
  • Program Counter
  • ALU
  • Display
  • EEPROM burner (need one to get display working)
  • RAM
The list of parts turned out to be unexpectedly long. Granted, I ordered some items that I think may be useful or fun to play around with, but still.

Also I couldn't locate some parts, so I had to think about alternatives:
  • There were no 74HC595 shift registers in stock, so I had to go with an alternative: 74HC594. They're pretty similar and for use in EEPROM burner there should not be any differences.
  • Then I couldn't locate anything resembling 74189 RAM chip. Went for 71256SA20TPG instead. It's a 32 kB SRAM, which feels like an enormous overkill, since I'm going to use just 16 bytes of it. But then again - it was not expensive at all. The RAM module, however, will be significantly different, compared to Ben's design
  • 28C16 EEPROMs also were not available. I went with 28C64 instead. Bigger capacity, more pins, but the idea should remain the same.
  • It turned out (a bit later) that neither I will be able to get 74HC161 counters. I went for 74HC163 instead. There's a difference how reset works, however. 161 resets immediately, while 163 requires an extra clock pulse for that. It actually may complicate things, but will see. Additionally I grabbed some 74HC191 up/down counters. Not completely sure, but those also could be an interesting alternative.

I placed my order with Farnell, and soon received good and bad news. Good was, I'll receive most of my order pretty soon. Bad news: unfortunately not all of it. Some DIP switches will be available in few months or so. But even worse: there was no timeline when I will get my hands on 74HC161 counters (I tried to order those on my first try). The switches were just "nice to have", but those counters are quite essential for my builds.

After a few exchanged e-mails with customer support, I cancelled both items and placed a new order for 74HC163. It's not ideal, but should be good enough.

There were warnings on the site about items being available from one or another warehouse for one or another kind of customers, but it seemed to be too much legal-speak for me. Customer support kindly explained it to me later.

Turns out, there are 2 warehouses: UK and Liege (which appears to be located in Belgium). Then there are VAT and non-VAT customers. And items from Liege are only available to VAT customers.

In short, as an individual, I'm non-VAT customer and should not bother with items available only from Liege.

But that being said, Farnell teamed up with UPS did a pretty good job of fulfilling and delivering my order. It took just one day for them to transport my order across all the Europe. Despite COVID-19 and everything. It was a lot quicker than ordering from local suppliers.

Now that I have my parts, I can finally start to build something.

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