Roy J. Tellason wrote: You may still have to dig through the data-sheets for $%@! got ya's with almost every cpu. Clock generation comes to mind as well as the IRQ logic on the Z80 is a bit trickry for non Z80 parts.

On Monday 16 June 2008 21:53, bfranchuk at jetnet.ab.ca wrote: Thanks. Define "small". I'm not familiar with many 6800 designs, but I was somewhat surprised to see how limited some parts are, like the 8085 in the "8085 Cookbook" where you could really get away with very little. OTOH, the c64 doesn't use any buffering _at all_ and yet the CPU in there seems to have little trouble driving 3 ROM chips, a set of 8 4164s, plus all the peripherals. I'm guessing that the Z80 is probably somewhere in between, and that the datasheet probalby won't give me the whole story anyhow. -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin

On Monday 16 June 2008 22:16, bfranchuk at jetnet.ab.ca wrote: Guess I should've mentioned wire-wrap in there someplace too... :-) -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin

Holger Veit wrote: for Z80 the consideration is clock speed (parts exist to 10mhz) and wich process (Nmos, NmosII or CMOS). Eactly. The biggest consideration is capacitive loading as CMOS draws no static current but the input still has capacitance that has impact with dynamic changes. so If you run the cpu slower than spec you can often "overload" the bus capacitively and have it work. Use care and make sure all the ground paths are very heavy for best results. For practical small systems using z80, 6502 or 8085 and modern memory buffering is generally not needed unless your driviing cable or going off board. Allison

On Tuesday 17 June 2008 03:57, Holger Veit wrote: Yeah, I'm not familiiar enough with the members of the 68xx family to know what the 6802 is all about without looking it up. But neither of these parts is what I'm into here anyway. I have some familiarity with the 8080, 8085, and z80. The 8080 with its requirement for support chips and multiple power supplies I'd rather avoid, the 8085 is okay but limited, and I have more z80 parts than anything else, so... I don't recall ever seein "8502" anywhere, the actual number in there being 6510, which has the onboard I/O port as being the major part of the differences as far as I'm aware. I don't know about differences in drive specifications and such. Nor do I have a clue as to where those 85xx numbers came from, only that I ran into some of them in the later c64s being used for CPU, SID, and VIC chips. Mostly though I have a lot of 6502s and 6522s familiar with those parts from the programming side of things though. Nor do I have any plans to support onboard video like the 64 did. Interesting to know. One thing I've always been curious about is when you look at the 64 schematics some of them shows lines on some of the connectors labeled "Z80" and "DMA" and I've never seen anything that actually used either of these. Hm. Perhaps I'll need to dig out what actual parts I have on hand and see who made them and which versions they are, then. Well, my inclination is to use what I have on hand, rather than buying stuff, if at all possible. What I have includes 2K and 8K static RAM (I wouldn't mind having some bigger parts :-), and an assortment of EPROMs of various sizes from 2716 on up, plus an assortment of Z80-family peripheral chips, and a lot of LSTTL. Maybe *some* 74HCT parts as well. I figure a CPU, one or two RAM chips (or more?), an EPROM, at least one serial chips, at least one parallel chip, perhaps a CTC and DMA, and we'll see where it goes from there. Just something to fool around with, mostly. The EPROM will get some kind of homebrew monitor and some code in there to load stuff by way of one or another port, I have no plans to tie a disk drive of any sort into this either. I'm particularly *not* inclined to try and go the route that I've seen a number of people go, where they want floppy drives, video, etc. essentially clonining what was out there to a large extent in the pre-PC days. I have plenty of PC hardware around if I want that sort of thing, and could even fire up my old Executive if I needed to get some of that feeling back again, but that's not where I'm inclined to go with this. -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin

BTW, anyone have a spare 6502C used in the Atari 5200 and Atari 400/800? My 5200 is broken :( I can't find a suitable spare :(

On Jun 16, 2008, at 10:07 PM, David Kane wrote: Here, what the 6800 can drive in terms of capacitance is another way of stating its output drive current capability. I'll expound for the benefit of those who haven't gotten their head around it yet. I thank our very own Tony Duell for helping *me* get my head around this many years ago, when my nice clean square waves were turning into deformed triangles as I tried to drive a big FET for an IR transmitter in a commercial product. This is a simplification, but it gets the point across. Think of it in terms of a signal changing state from 0 to 1. CMOS chips are FET-based, and the input of a CMOS logic gate typically goes to the gate ("gate" in FET terms, not logic terms) of a FET. The FET's gate is essentially a tiny capacitor. To turn the FET on, one must charge that capacitor. So, you need to raise the voltage on the FET's gate from ~0V to ~2V (the 74HCT 0-1 threshold according to Fairchild's AN-368 app note). The higher the capacitance of that logic gate's input (which is the gate capacitance of the input FET, typically Ciss on transistor datasheets) the more current it'll take to charge it to a the 0-1 threshold voltage in a given amount of time. If the capacitance is lower, it'll take less current. Now, recall that capacitances in parallel add up...so if the input capacitance of (say) a 74HCT245 is 3.5pF (from the datasheet), if you put five 74HCT245 inputs on a bus line, the total capacitance (excluding PCB traces, etc) is 5*3.5 = 17.5pF...requiring more drive capability from whatever is driving that bus line. So if the drive capability is insufficient, the rise time of the pulse will lengthen, and turn that nice sharp rising edge into a long sweeping transition, screwing up the timing and confusing lots of things. -Dave -- Dave McGuire Port Charlotte, FL