Hi All,

I have an UM6502 CPU from UMC. Since it's virtually impossible to buy a CMOS 6502 in my country (yes, it can be bought with international shipment, but the price is "horrible" then), and I do have an UM6502 (MOS), I am thinking to build a simple SBC using it as my first 6502 project. Does anybody have any comment about this UM6502, which can help? For example I read about internal heating problems of some MOS 6502s, etc.

My other question: the specification of UM6502 states that one TTL can be driven. However the SRAM and EEPROM I (will) have are CMOS ones, however their specifications write that TTL comaptibility is OK. But now I am thinking if it's really true if I connect CMOS parts with a MOS CPU like this? Also, should I use any bus drivers for data&address bus or UM6502 will ok to do it? I'd happy to have a simplier design with direct connection though I am a little confused here that memory chips are about having TTL and CMOS logic level compatibility, but still eg 74 series of logic ICs have HCT ones for TTL compatibility if HC is not well suited for this task. Besides the memory some other parts would be connected as well, like LCD module with 8 bit data bus, etc.

So: having a TTL MOS CPU, CMOS memories and maybe 74HCT for address decoding & glue logic.

Any feedback is welcome, thanks!

I have a UM6502, and I got it from ebay.
I had no issues at all when building my SBC.
It works fine with TTL and CMOS devices, in fact I got it to work on 4MHz, and the ic is declared at 1MHz. I happen to have lots of different NMOS 6502, and even the CM630P clone, and all of them work properly on 1MHz.

_________________
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?

When I used LS parts, I had some issues with one LS ic, so I replaced it with HS, and the problem was solved.

First, sorry for the mess. Yes, I meant NMOS, not the brand (MOS). However, I'm still confused as many resources mention "CMOS logic levels vs TTL" etc, but nothing can be found if NMOS/CMOS have any difference at all from the view point of connecting them onto a common bus system (logic level voltages). The other thing made me meditating on this topic that (my) UM6502 being an NMOS CPU still talks about the "one TTL load driving ability" (in the specification). Since I don't want to put TTL parts into the design (CMOS/NMOS only) what does it mean for me? I don't want to overload&fire my UM6502 (which was hard to get: it's really not easy to get _any_ 65xx like CPU, unlike Z80 which can be bought in almost every shops even in my country, Hungary). I am just guessing that "one TTL load" does not mean literally that you have to drive TTL IC, it is just a notion to give a hint about current can be sourced/sinked at max or so. Am I right with this or totally wrong ... I guess both of CMOS and NMOS use FETs having much greater impedance than a TTL gate so if an IC can drive one TTL load, it really mean dozens for CMOS/NMOS ICs.

Secondly; yes, I know about 6502 primer, it was the first resource I found when I started to seek for information on the web about my planned 6502 project. It's a really usefull and very detailed series of pages about many topics on designing small 6502 based systems.

As for clock, 1MHz is OK for me, because my UM6502 is specified for that, and also because my somewhat beginner-like soldering/wiring abilities, I guess my chance for success is much higher at lower clock frequency

So true. I would love to have 65816 but eg mouser (as a wdc distributor) asks for 40EUR for shipment even if I want only one 65816. Ok, if I order dozens of ICs, it's not so bad, but I don't need bigger quanty (and I don't have much money for my hobby unfortunately), also maybe EU policy would require to pay taxes if the shipped goods' value are higher than 20EUR, or something similar (I don't know, I haven't even tried)? The new idea to exploit friends' friend living in USA to buy some ICs and bring to my country when they visit home Really it seems there is no "normal" way to buy anything from USA, since that would be horrible expensive. On the other side, from China you can order things on "bizarre cheap" price ... Basically even the same things, I've just found some online shops from China having 65816 ... Still I am a bit nervous about this (trust in no-name China companies).

_________________
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?

Well, I am from Croatia, so I have the identical issues as you.
But then I got a PayPal account, and went on ebay and bought all of the 65xx ic that I needed. Old NMOS IC are really cheap on ebay and other online shopping sites. So if you want to build something, and not spend too much money, I would recommend going to ebay and getting old NOS(New Old Stock) IC, also shipping is a few dollars, and sometimes even free.

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

Thanks for the tip, honestly I've never tried to buy anything on e-bay yet ... Also it's a bit surprising for me that it's worth for someone to sell an IC for a low price even with the ship cost is included sometimes?

Sellers that usually sell such IC have big warehouses full of all sorts of old IC that remain from the original era. Once I bought a MC6875 clock generator IC, and when I got it it looked brand new, unbent pins and no sign of wear. All of the IC that I got from ebay are in proper working order, I never got a faulty IC. Another good thing about ebay is their policy where if you get a faulty/wrong item you can get your money back, or the seller can send you another item. Also if you don't receive your package you are always going to be refunded. That is why I like ebay, unlike some other websites that don't offer such policy.