Beginner Questions: RCBus vs RC2014 , Z80 vs Z180, and Interoperability

[Scott Pezza]

Hi folks,

I am at the beginning of my journey and was hoping to elicit some advice to start off on the right foot. At the moment, it seems like there is a greater variety of RC2014 40-pin cards for things like audio and video than for RCBus. I'm sure this will change over time. I like the greater potential for RCBus, but don't know where to start because of apparent difference in board variety.

This leads to a few questions, specifically:

1. Will RC2014-compliant 40-pin cards work on a RCBus 80-pin backplane? Since RC2014 is a subset of RCBus, I would hope/expect that to be the case.
2. Will Z80-focused cards work with a Z180 CPU? If Z180 is an extension of Z80, it would make sense, but I feel a bit less comfortable here.

If the answer is yes to both, then a "future-proof" approach would seem to be using an RCBus 80-pin backplane, Z180 cpu board, 80-pin versions of the main components (memory, I/O, etc.), and then mixing in RC2014 boards for audio and video where 80-pin variants don't currently exist.

Would that be a reasonable approach? Am I setting myself up for any common problems that are obvious to those with more experience?

Thanks!

Scott

[Tadeusz Pycio]

Hi Scott,

The RCBus standard is RC2014-compatible by design, so any RC2014-compliant module will operate on the RCBus. In the case of the Z180 and Z80-dedicated modules, the key parameter is their maximum clock frequency. A number of ICs are not capable of stable operation above the threshold for which they were designed, and it is important to remember that the standard Z180 clock is 18.432MHz instead of 7.3728MHz as for the Z80.

[Shawn Reed]

Scott,

This is a disease, you are about to find out that building just one system is simply not possible. It is just too much fun getting the system all setup and running. 

I started with an RC2014 Pro a few years ago and then Steve's original Z50 Bus because it sounded interesting then life happened and I was a way a couple years.  Recently I was able to devote some time into the Z50Bus system and also got caught up on the RCBus standard.  So of course I had to order another system thinking I full system would provide me with ample fun building over a couple months perhaps.  Turns out the system was fully assembled and running in 4 evenings. 

I enjoyed it so much I was wondering if I should check to see if there was interest in having systems built and tests as turnkey for anyone not interested in soldering. I have dismissed that idea with the assumption that logistics and costs would just be too impractical.  

I have spent some time over the past couple weeks testing Z-System on RomWBW and some developing on target with HITech-C and ZDE. Last weekend I dedicated to z88dk using VS Code. This weekend I have switch to Steve's Workbench and  SCM 1.3 testing our the Idle events BIOS API. I am trying to figure out where I want to spend some time developing and hopefully contributing back.

-Shawn

[Scott Pezza]

Thank you both for replying so quickly! I feel much better prepared for what I now know is likely the first system of many. :)

-Scott

[Alan Cox]

> Would that be a reasonable approach? Am I setting myself up for any common problems that are obvious to those with more experience?

The cards you will have speed problems with when using Z180 are
generally the Zilog companion parts (SIO, PIO, CTC, DMA,KIO) as these
have to be clocked at the CPU clock, or very carefully at an exact
divider. RC2014 assumes the former and they don't have circuitry for
the dividing trick. Other I/O stuff generally works reliably as ROMWBW
uses the wait state feature on the Z180 to set wait states on the I/O
bus cycles.

Of the cards I've dealt with the table is something like this

Z80SIO - replace with 16x50 UART if needed (Z180 has two ports onboard anyway)
Z80PIO - for simple GPIO use SC129
Z80DMA - not needed - Z180 has on chip DMA
Z80CTC - usually not needed - Z180 has on chip timers, and 16x50 has
its own baud rate generator
TMS9918A - needs longer delay loops in the software
Propeller Graphics - needs longer delay loops if not using halt signal

Of the other commonly used parts some generate clocks by dividing the
7.37MHz down and not all have dividers for 18.432 so they sometimes
need a bit of hacking. Some of the older sound cards had that problem.

Alan

[Bill Shen]

Z80KIO is combination of SIO, PIO, and CTC in one chip .  Z80KIO has its own 3.68MHz baud clock and can handle CPU clock as high as 30MHz, so it can work with both 7.37MHz RC2014 as well as 18.4MHz Z180 .
  Bill

[Scott Pezza]

Thanks, Alan and Bill!

I took it easy on myself and started off with a Z80 cpu. When I have more knowledge (and maybe courage) I'll experiment with the Z180. Hopefully this project is the first of many.

-Scott

[Shawn Reed]

So what you are all saying is that I also need to build a Z80 RCBus... yea ok I can do that.

[Mark T]

Or put a z50 to RCBus adapter on your z50 bus system, add a few RCBus modules and then decide later if you should have a separate RCBus only system.

[Justin Skists]

/me shiftily hides multiple rc2014-based systems behind my back...

I don't know what you're talking about. ;-)

Justin

[Steve Cousins]

You know this a support group for the addicted, right?

If you haven't got more than one system yet, save yourself. 

Get out while you still have a chance.

Steve

[Bill Shen]

Well!  You are the one to talk while designing your 100th RCBus board, or is it 200th board?  Of course I’m in no position to criticize while sending away 4 retro designs just this morning.  Too late for us addicts, might as well wallow in it.

Bill

[Bill Shen]

While it is hot off the press (I sent off the designs 2am this morning and JLCPCB replied with an email of my boards), let me demonstrate how deep the addictions are.  These are the 4 designs, 65all (all-in-1 6502 standalone computer), EPM570 prototype board (1st 3.3V designs), Tiny040 (exploratory 68040 design), and IP940Base (motherboard for IP940– a 68040 mezzanine board).  Every one of these boards has a classic RC2014 expansion bus.  RC2014 and RCBus are simply too useful and got abused by people like your truly.

  Bill

[Tadeusz Pycio]

My rehab treatment is working, I have only designed 4 modules this year. :-D

[Bill Shen]

The year is still young.  You’ll be relaxing in a park watching some guy juggling and suddenly you’d say, “what ho, I can do that with 74LS157 multiplexer!”, and off to the drawing board you go.  Addiction is sneaky like that.

[Scott Pezza]

I'm honored to have an all-star group of folks responding here!

I look forward to moving from the "what the heck does this do?" to the "how do I make something to do X?" stage of this hobby/obsession/addiction.

-Scott

[Stefan V. Pantazi]

A little bit late to join the fray but I concur, the condition is real. The stages seem fairly well established. One starts with wondering if they can repair their old gear to satisfy their nostalgic tendencies. One thing leads to another, maybe building a replica using new techniques and tools followed by "improvements". After a short while, the experimental stage sets in, similar to the earlier mentioned "can I make this do X" only to realize that there are so many existing designs that many of you fine folks are putting out and that we can try and build to learn and to keep feeding the addiction. I suspect the "design" stage of the disease sets in later as one is well versed and the condition may have become chronic.

I personally am at the wonderful (and fairly expensive) experimental stage and enjoy building existing designs while adding various simple twists and tweaks. I will be posting a summary for my build of a SC7xx series computer with many modules  including a mixed bag of RC2014 modules. In keeping with the current symptoms of my affliction, I not only just built a bunch of them to be combined in various ways, I also had success using LS class ICs not HCT with some small changes in th epull up resistor values. Many thanks to Steven Cousins, Bill Shen, Phillip Stevens and Ed Brindley as well as to the many others that designed RC2014 modules and made them available. 

Stefan