Total newb questions about the SCC hardware platform
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Timmy Austin
Aug 6, 2025, 2:57:11 AMAug 6
to retro-comp
I am about to sound like the biggest amateur but I have a bunch of very basic questions to get me going in the right direction. A quick about me; I started programming on a C64 at a very young age. I have been soldering for 35 years. I whipped together a RetroChipTester that fired up on the first go. That is to say, I can solder. At the end of this post is seriously unneeded information and is there just to tell you how I ended up here. Thank you for any help you can give me so I can get back into this!
1) As best I can determine there are 4 Small Computer Central "series". There is the 100 series that seems to be older boards from back before some kind of drama that played out. This series has 3 "form factors" (40, 41-60 and 80 pins) and are all legacy-ish boards? Then there is the 500 series that is based on the Z50 bus and are not really part of the 40-80 pin specs (though the can be adapted by boards). Now there is the newer 600 and 700 series. It seems to me that the 600 series is a 40 pin RCbus reworking of the "original" bus and the 700 series is the expanded 80 pin bus of the 600 series. Does this all seem correct?
2) What is the basic difference in terms of the 600 and 700 series? I mean obviously more is broken out to the bus but why the need the new 600 series if the 700 series is a marked improvement in functionality? Is it just a matter of simplicity over complication or is there other concerns which were taken into account?
3) With this said, as I understand it the RCbus is largely directly compatible with all three series (save for the 500 series) So, and I am not saying that this is the setup I am considering, I can take a 702 backplane, slap a 142 power module, a 601 CPU module, a 714 RAM/ROM module and a RC2014 dual serial module in and have a working system? It's really just a matter of putting the 40 pin modules in the right locations?
4) If the above is true then what is reasoning (not a criticism, but a question) for most of the duplicated 80 pin modules? For example the 703 and 614 power modules or the 715 and 604 CF modules. Obviously the CF modules have a different footprint but other than the 604 having a extra cap they appear identical on the bus, save for the power pins being on the front and rear connector. A large benefit of the 80 pins is the functionality, for example I can see where the 610 and 705 serial modules differ, while using the same ACIA, and why the 700 series has a lead here. What I can't figure out is what the benefit is to the 600 series if the 700 series can do everything that it can do? Should I build 600 modules, when the functionality is the same, for the sake of combability with 40 pin backplanes and ignore the 700 series modules?
5) I think I am leaning towards a 126 for a Z180 motherboard with expansion. I have no experience with the Z180 but I figure I should get one going before the CPU completely disappears. Would the 126 be a good choice for the Z180 or should I go with a 700 series modular system?
6) I also want a Z80 system that actually works. I am thinking the 720 is a good jumping off point for the same reason as above. Is that currently the most recommended platform for the Z80 with future expandability?
7) Finally, at least for hardware, I am also going to do a modular 700 series backplane to try to get some of my old cards working (see below if you're interested). They are all 40 pin cards but I figure that an 80 pin backplane would give me more options in the future. Does that seem reasonable?
I also would like to give a big thank you to Steve for designing, collating, and hosting all of this hardware. Also, a big thank you to Tadeusz for all of the designs I have seen you crank out. Also, everyone else on here for the information I have been digging through while I figure out what I want to do, thank you all too!
Thanks for reading that wall of text!
*** Errata
About a decade ago I jumped in on a platform for the Z80 and ordered up a rather basic kit. I soldered everything up and it worked for a few weeks and then the problems started. I ended up ordering another kit from the same place just to troubleshoot (I did not yet own an oscilloscope). First thing was the tiny clock board was junk and had stopped working, when that was replaced it worked again. In the meantime I had been moving boards around and quickly discovered that the basic serial board had better be next to CPU board or I was gonna be in for a confusing night. That's just a couple of the problems, so into the box of completed kits it went to be forgotten. I never ever got off the ground with the software side as the hardware was just too unreliable.
Now here I am 10 years later and the bug is back in the rear. The smaller of the two backplanes had the tiniest via I have ever see which carried the entire ground rail for the bus and that had lost continuity. A bodge wire got power back up but the signals on the scope were are messed up on both backplanes I had. I discovered the Small Computer Central project and it intrigued me. After digging pretty deep through this forum I read a reply (I am sorry, I forgot your name) that said during the RCbus spec discussion that it may confuse newcomers and boy was he right. I love the idea of really well documented hardware, with a multitude of choices, but I got lost in a hurry with the differences and needs.
1) As best I can determine there are 4 Small Computer Central "series". There is the 100 series that seems to be older boards from back before some kind of drama that played out. This series has 3 "form factors" (40, 41-60 and 80 pins) and are all legacy-ish boards? Then there is the 500 series that is based on the Z50 bus and are not really part of the 40-80 pin specs (though the can be adapted by boards). Now there is the newer 600 and 700 series. It seems to me that the 600 series is a 40 pin RCbus reworking of the "original" bus and the 700 series is the expanded 80 pin bus of the 600 series. Does this all seem correct?
2) What is the basic difference in terms of the 600 and 700 series? I mean obviously more is broken out to the bus but why the need the new 600 series if the 700 series is a marked improvement in functionality? Is it just a matter of simplicity over complication or is there other concerns which were taken into account?
3) With this said, as I understand it the RCbus is largely directly compatible with all three series (save for the 500 series) So, and I am not saying that this is the setup I am considering, I can take a 702 backplane, slap a 142 power module, a 601 CPU module, a 714 RAM/ROM module and a RC2014 dual serial module in and have a working system? It's really just a matter of putting the 40 pin modules in the right locations?
4) If the above is true then what is reasoning (not a criticism, but a question) for most of the duplicated 80 pin modules? For example the 703 and 614 power modules or the 715 and 604 CF modules. Obviously the CF modules have a different footprint but other than the 604 having a extra cap they appear identical on the bus, save for the power pins being on the front and rear connector. A large benefit of the 80 pins is the functionality, for example I can see where the 610 and 705 serial modules differ, while using the same ACIA, and why the 700 series has a lead here. What I can't figure out is what the benefit is to the 600 series if the 700 series can do everything that it can do? Should I build 600 modules, when the functionality is the same, for the sake of combability with 40 pin backplanes and ignore the 700 series modules?
5) I think I am leaning towards a 126 for a Z180 motherboard with expansion. I have no experience with the Z180 but I figure I should get one going before the CPU completely disappears. Would the 126 be a good choice for the Z180 or should I go with a 700 series modular system?
6) I also want a Z80 system that actually works. I am thinking the 720 is a good jumping off point for the same reason as above. Is that currently the most recommended platform for the Z80 with future expandability?
7) Finally, at least for hardware, I am also going to do a modular 700 series backplane to try to get some of my old cards working (see below if you're interested). They are all 40 pin cards but I figure that an 80 pin backplane would give me more options in the future. Does that seem reasonable?
I also would like to give a big thank you to Steve for designing, collating, and hosting all of this hardware. Also, a big thank you to Tadeusz for all of the designs I have seen you crank out. Also, everyone else on here for the information I have been digging through while I figure out what I want to do, thank you all too!
Thanks for reading that wall of text!
*** Errata
About a decade ago I jumped in on a platform for the Z80 and ordered up a rather basic kit. I soldered everything up and it worked for a few weeks and then the problems started. I ended up ordering another kit from the same place just to troubleshoot (I did not yet own an oscilloscope). First thing was the tiny clock board was junk and had stopped working, when that was replaced it worked again. In the meantime I had been moving boards around and quickly discovered that the basic serial board had better be next to CPU board or I was gonna be in for a confusing night. That's just a couple of the problems, so into the box of completed kits it went to be forgotten. I never ever got off the ground with the software side as the hardware was just too unreliable.
Now here I am 10 years later and the bug is back in the rear. The smaller of the two backplanes had the tiniest via I have ever see which carried the entire ground rail for the bus and that had lost continuity. A bodge wire got power back up but the signals on the scope were are messed up on both backplanes I had. I discovered the Small Computer Central project and it intrigued me. After digging pretty deep through this forum I read a reply (I am sorry, I forgot your name) that said during the RCbus spec discussion that it may confuse newcomers and boy was he right. I love the idea of really well documented hardware, with a multitude of choices, but I got lost in a hurry with the differences and needs.
Steve Cousins
Aug 6, 2025, 7:24:25 AMAug 6
to retro-comp
Welcome to the not so simple world of retro computers.
Answers:
1/ Spot on. Really good analysis of my offerings.
2/ Yes, it is mainly a matter of wishing to create one series to take full advantage of the 80-pin RCBus (SC700 series) and another series (SC600 series) to keep things a little simpler and have less soldering. More below.
3/ Except for a few clashes of addresses etc. you can mix and match in the way you describe. Generally, the modules can be placed in any locations.
4/ See below.
5/ SC126 is still a good option in my opinion. Essentially it includes the functionality of a number of modules and is expandable using many of the RCBus modules.
6/ Like SC126, SC720 can function as a single board computer but is expandable with RCBus modules. It is the Z80 version of SC126. It is my opinion that it is a good starting point.
7/ Yes, that is indeed reasonable.
I have produced rather a large range of designs with much duplication. I like designing stuff and got a bit carried away. There isn't a strong justification for many of them. So, yes, the range is confusing. If I was more motivated by commercial success I probably would have a simple range in only one PCB colour and would benefit from the economy this would bring.
So how did I get here?
Back in about 2016 I decided I wanted to get back into simple (retro) computers. I rather fancied trying to create my own CPU from 74 series logic and ROMs. I wanted to do everything from scratch and write my own assembler and simulator. This plan got as far as my unfinished Small Computer Workshop (SCW) IDE. In order to implement this big plan in stages, I initially made the SCW IDE compatible with the Z80. I spotted the RC2014 system and decided that starting with this system made sense as a stepping stone to a system of my own design, so I purchased a RC2014 Pro kit. By this point I started getting drawn into the RC2014 community and my home made CPU project got 'delayed'. Also, I didn't spend much time debugging and completing SCW. SCW worked well enough for me to develop code for my RC2014 Pro and the result was the Small Computer Monitor (SCM). I also prototyped my own single board computer (or perhaps more accurately a motherboard) which you'll find on my website as SC101.
About this time I realised PCB manufacture had become cheap enough for hobby budgets. I noticed the RC2014 lacked support for Z80 family CTC and PIO devices, so I designed SC102 (Z80 CTC) and SC103 (Z80 PIO). I completed the set with my own Z80 SIO module, SC104. When others showed interest I offered my spare PCBs. Before I could say "this wasn't the plan" I found myself offering kits on Tindie. I went on to develop all sorts of kits for RC2014 and Z50Bus, giving each a number in the SC100 range. This evolved into a random mess of number assignments.
When the RCBus specification was drawn up I decided to start a new range to take advantage of the 80-pin bus. Thus the 700 series. After I'd created a decent 80-pin range I decided to tidy up the messy 100 series, largely by producing new designs specifically for the 40-pin RCBus. Thus the 600 series. The SC600 series wasn't necessary, I just wanted to do it.
If you settle on the 80-pin RCBus you can supplement it with modules designed for the 40-pin RCBus or the RC2014 bus. The only issues I see with the mix and match approach are:
1/ The 40-pin modules touch the jumpers found between bus sockets on the 80-pin backplanes. This hasn't caused any problems I'm aware of but you might like to build the backplane with out some of the jumper pins fitted to allow 40-pin modules to be fitted without this concern.
2/ The mounting holes found on most modules do not line up as the commonly used bus header pins are a different profile for 40-pin and 80-pin modules.
Which bus is best?
Well I've changed my mind a few times on that. Initially I assumed the RC2014 enhanced bus (41 to 60 pins) was best, but I didn't like the lack of support for the Z80 mode 2 interrupt daisy chain or the inconsistent number of pins. The modules are also difficult to remove without bending pins. The Z50Bus fixes these issues. It has a module PCB wider than the bus connector, giving an overhang to get your finger tips under. The 40-pin bus modules are relatively easy to remove as the commonly used bus connector has the module PCB overhang the bus socket by enough to get a finger tip under. When the RCBus specification was drawn up the 80-pin bus seemed the best. While it is the most functional and most future proofed it does have some issues. There's more soldering to do and the modules are hard to remove. I found myself preferring the 40-pin bus due to its simplicity and easier module removal.
When I designed the 600 series I thought carefully about how to get the best out of it without breaking compatibility. There are differences in some of my 40 and 80-pin designs to make best use of the bus features available. One example is serial modules. With only one clock source available on the 40-pin bus it is very attractive to have a flexible baud rate generator on the serial module.
Single board or fully modular?
The bus connectors used on all these systems are cheap and cheerful. They aren't ideal. Having lots of modules adds to the risk of reliability issues. It makes sense to have all the 'standard' features on a single board with expansion sockets for other functions. On the other hand, a fully modular system is more flexible and has a consistent look.
Essentially, my offerings are those of an enthusiast rather than being commercially motivated.
I have come to the conclusion the vast majority of people are well served by the 40-pin RCBus. In fact, it is currently my favourite for fully modular Z80 systems. Most of the time I use SC720 for Z80 work and SC126 for Z180 work. Both can be greatly expanded with either 80-pin backplanes or simpler 40-pin backplanes. Z80 systems have the best compatibility with the wide range of modules from different suppliers. The Z180 generally operates at 18.432 MHz, rather than 7.3728 MHz, leading to some compatibility issues.
Steve
Answers:
1/ Spot on. Really good analysis of my offerings.
2/ Yes, it is mainly a matter of wishing to create one series to take full advantage of the 80-pin RCBus (SC700 series) and another series (SC600 series) to keep things a little simpler and have less soldering. More below.
3/ Except for a few clashes of addresses etc. you can mix and match in the way you describe. Generally, the modules can be placed in any locations.
4/ See below.
5/ SC126 is still a good option in my opinion. Essentially it includes the functionality of a number of modules and is expandable using many of the RCBus modules.
6/ Like SC126, SC720 can function as a single board computer but is expandable with RCBus modules. It is the Z80 version of SC126. It is my opinion that it is a good starting point.
7/ Yes, that is indeed reasonable.
I have produced rather a large range of designs with much duplication. I like designing stuff and got a bit carried away. There isn't a strong justification for many of them. So, yes, the range is confusing. If I was more motivated by commercial success I probably would have a simple range in only one PCB colour and would benefit from the economy this would bring.
So how did I get here?
Back in about 2016 I decided I wanted to get back into simple (retro) computers. I rather fancied trying to create my own CPU from 74 series logic and ROMs. I wanted to do everything from scratch and write my own assembler and simulator. This plan got as far as my unfinished Small Computer Workshop (SCW) IDE. In order to implement this big plan in stages, I initially made the SCW IDE compatible with the Z80. I spotted the RC2014 system and decided that starting with this system made sense as a stepping stone to a system of my own design, so I purchased a RC2014 Pro kit. By this point I started getting drawn into the RC2014 community and my home made CPU project got 'delayed'. Also, I didn't spend much time debugging and completing SCW. SCW worked well enough for me to develop code for my RC2014 Pro and the result was the Small Computer Monitor (SCM). I also prototyped my own single board computer (or perhaps more accurately a motherboard) which you'll find on my website as SC101.
About this time I realised PCB manufacture had become cheap enough for hobby budgets. I noticed the RC2014 lacked support for Z80 family CTC and PIO devices, so I designed SC102 (Z80 CTC) and SC103 (Z80 PIO). I completed the set with my own Z80 SIO module, SC104. When others showed interest I offered my spare PCBs. Before I could say "this wasn't the plan" I found myself offering kits on Tindie. I went on to develop all sorts of kits for RC2014 and Z50Bus, giving each a number in the SC100 range. This evolved into a random mess of number assignments.
When the RCBus specification was drawn up I decided to start a new range to take advantage of the 80-pin bus. Thus the 700 series. After I'd created a decent 80-pin range I decided to tidy up the messy 100 series, largely by producing new designs specifically for the 40-pin RCBus. Thus the 600 series. The SC600 series wasn't necessary, I just wanted to do it.
If you settle on the 80-pin RCBus you can supplement it with modules designed for the 40-pin RCBus or the RC2014 bus. The only issues I see with the mix and match approach are:
1/ The 40-pin modules touch the jumpers found between bus sockets on the 80-pin backplanes. This hasn't caused any problems I'm aware of but you might like to build the backplane with out some of the jumper pins fitted to allow 40-pin modules to be fitted without this concern.
2/ The mounting holes found on most modules do not line up as the commonly used bus header pins are a different profile for 40-pin and 80-pin modules.
Which bus is best?
Well I've changed my mind a few times on that. Initially I assumed the RC2014 enhanced bus (41 to 60 pins) was best, but I didn't like the lack of support for the Z80 mode 2 interrupt daisy chain or the inconsistent number of pins. The modules are also difficult to remove without bending pins. The Z50Bus fixes these issues. It has a module PCB wider than the bus connector, giving an overhang to get your finger tips under. The 40-pin bus modules are relatively easy to remove as the commonly used bus connector has the module PCB overhang the bus socket by enough to get a finger tip under. When the RCBus specification was drawn up the 80-pin bus seemed the best. While it is the most functional and most future proofed it does have some issues. There's more soldering to do and the modules are hard to remove. I found myself preferring the 40-pin bus due to its simplicity and easier module removal.
When I designed the 600 series I thought carefully about how to get the best out of it without breaking compatibility. There are differences in some of my 40 and 80-pin designs to make best use of the bus features available. One example is serial modules. With only one clock source available on the 40-pin bus it is very attractive to have a flexible baud rate generator on the serial module.
Single board or fully modular?
The bus connectors used on all these systems are cheap and cheerful. They aren't ideal. Having lots of modules adds to the risk of reliability issues. It makes sense to have all the 'standard' features on a single board with expansion sockets for other functions. On the other hand, a fully modular system is more flexible and has a consistent look.
Essentially, my offerings are those of an enthusiast rather than being commercially motivated.
I have come to the conclusion the vast majority of people are well served by the 40-pin RCBus. In fact, it is currently my favourite for fully modular Z80 systems. Most of the time I use SC720 for Z80 work and SC126 for Z180 work. Both can be greatly expanded with either 80-pin backplanes or simpler 40-pin backplanes. Z80 systems have the best compatibility with the wide range of modules from different suppliers. The Z180 generally operates at 18.432 MHz, rather than 7.3728 MHz, leading to some compatibility issues.
Steve
Timmy Austin
Aug 6, 2025, 9:37:31 AMAug 6
to retro-comp
Normally I would you call an absolute gentlemen but knowing that you are from the UK....you sir are a bloody legend! Thank you very much for the very detailed response! That hit every note I had on the platform. It perfectly answered every doubt, and question, I had. Also, this quote, "The SC600 series wasn't necessary, I just wanted to do it" is the best reason to do anything!
I had actually given that spacer thing a few fleeting thoughts while looking into this all. I think that with the ubiquity of 3D printing I may be able to work something out that makes the spacer more robust.
I am excited again to get lost down this rabbit hole again in the near future.
Thank you again for all of your work. I know that I am not the only one who sees it and everyone who does appreciates it.
Mark Pruden
Aug 7, 2025, 9:24:38 AMAug 7
to retro-comp
> 5) I think I am leaning towards a 126 for a Z180 motherboard with expansion. I have no experience with the Z180 but I figure I should get one going before the CPU completely disappears. Would the 126 be a good choice for the Z180 or should I go with a 700 series modular system?
This is the choice i went with also, but I would make one suggestion. You need to invest in CF storage add on card. While the SD card interface (present on the SC126) works it is basically transferring over a serial bus, as compared to CF with is an 8 bit parallel bus. As a consequence the performance of CF is significantly faster.
Alan Cox
Aug 7, 2025, 9:37:47 AMAug 7
to Mark Pruden, retro-comp
SC126 is a nice board on the whole although be aware the i2c can't cope with clock stretching and using more than one SPI device needs a small add on fix board. Otoh the bonus of the fix is you get 3 or 4 SPI devices!
In terms of speed whilst the SPI SD card is a bit slower it's also a lot more reliable than many rc2014 CF adapters some of which have timing errors and inadequate power and grounding.
CP/M 3 is much faster for IO in general as it fixed the worst of the CP/M 2 bottlenecks (CP/M 2 really being designed when floppies were as fast as people went). Even the SD card on CP/M 2.2 is way way faster than any historical CP/M box.
If you absolutely must have max speed then the fastest option is Z180, a decent CF adapter and modding the SC126 so DMA works, but it's insanely fast versus what was historically possible!
Alan
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midc...@gmail.com
Aug 7, 2025, 3:31:24 PMAug 7
to retro-comp
I started with a SC126 kit. It has a lot of features. I initially missed 2 solder connections building it but after that, it just came up running with no problems. After awhile, I started purchasing SC700 boards (mostly bare and proto boards). So the SC700 80 pin backplane system is what I tinker around with and sometimes temporarily mess it up. However, the SC126 is always there and working and I use it to flash ROMs.
Timmy Austin
Aug 7, 2025, 5:13:21 PMAug 7
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So I was planning on doing a compact flash but I am curious about the "small add on fix board" that you mentioned etched? What is it and were can I look into it to see why the SPI limitation exists.
....And another thought about hardware that popped into my head. I generally socket ICs but ROMs, in this type of situation, tend to get removed often. Neither the SC720 or the SC126 have the clearance for a ZIF socket, right? I absolutely dread unseating DIPs in sockets. I have the luck of Murphy.
Alan Cox
Aug 7, 2025, 5:30:08 PMAug 7
to retro-comp
---------- Forwarded message ---------
From: Alan Cox <etched...@gmail.com>
Date: Thu, 7 Aug 2025, 22:29
Subject: Re: [retro-comp] Re: Total newb questions about the SCC hardware platform
To: Timmy Austin <ourcr...@tomamore.com>
From: Alan Cox <etched...@gmail.com>
Date: Thu, 7 Aug 2025, 22:29
Subject: Re: [retro-comp] Re: Total newb questions about the SCC hardware platform
To: Timmy Austin <ourcr...@tomamore.com>
It is on my hackaday. Basically the SC126 powers on with both SPI devices selected and that can damage them, as can a bad IO write. The fix just uses the two pins as a mix so you can't select two devices at once. It also mixes the input line so badly behaved SPI devices like SD cards will share
You can stack a zif on a socket or two , clunky but workable. It also has two ROM sockets so you can boot one, lock the CPU running in RAM and then carefully flip the jumper and flash a section
Alan
To view this discussion visit https://groups.google.com/d/msgid/retro-comp/f8907eba-6454-4f9a-9328-e5999a7747d5n%40googlegroups.com.
Greg Holdren
Aug 7, 2025, 8:01:58 PMAug 7
to retro-comp
Here is more info on the SPI SD cards adapters shipped with the SC126. They could could be improved a bit. Here is another thread that addresses the issue and corrects the adapter so that is it isn't always driving the MISO line all the time. The SPI port can then be shared.
Greg
Timmy Austin
Aug 7, 2025, 8:20:49 PMAug 7
to retro-comp
Thank you for the link Greg. I also found the Hackaday post in there. We are getting deeper into the platform now. Unless I am missing something, and that is very much possible, the need for a 153 logic chip is to prevent conflicts between multiple SPI devices. Though, if I don't intend to use more than two SPI SD cards, this should not be an issue? It appears RomWBW can support at least the 2 onboard SPI devices with a rather simple adjustment to the rom, correct?
Greg Holdren
Aug 7, 2025, 8:45:48 PMAug 7
to retro-comp
Sure. If you intend to to only use both of the SD card SPI ports on the SC126 then you don't need the '153. (haven't pulled up the Alan's expansion SPI board schematics, I think this is what '153 refers too).
All you need to do is the SD card adapter mod to connect the module's '125 pin (MISO) U1D pin 13 from being enabled all the time (Grounded) and connect to the /CS pin. So if /CS is low then MISO will drive the selected SD card. SW will drive one /CS at a time. Do the mod for both SD card adapters. Enable ROMWBW for both interfaces as noted by Wayne.
Greg
Timmy Austin
Aug 8, 2025, 5:45:43 AMAug 8
to retro-comp
Excellent! Thank you!
And yes, I was referring to Alan's schematic from his hackaday with the 153. It allows for more SPI devices and I'll keep it back in the trap if I ever find myself needing that many devices. Also, funny enough, I am not a dedicated hardware guy. I ended up looking up the schematic for a typical SD hardware module and discovered the "LVC" designation for the 74X series. It completely makes sense that a low voltage CMOS version would exist, I have just have never seen it. I would have died on the hill that LS/HC/HCT are the only types of logic chips there are. lol.
Alan Cox
Aug 8, 2025, 7:13:48 AMAug 8
to retro-comp
On Fri, 8 Aug 2025 at 01:45, Greg Holdren <greg.h...@gmail.com> wrote:
Sure. If you intend to to only use both of the SD card SPI ports on the SC126 then you don't need the '153. (haven't pulled up the Alan's expansion SPI board schematics, I think this is what '153 refers too).
The 138 does the muxing to stop selecting two devices at once. I added the 153 so you didn't either have to find properly made SD adapters (not the arduino shit everyone pedals) or modify the SD modules.
MISO will drive the selected SD card. SW will drive one /CS at a time. Do the mod for both SD card adapters. Enable ROMWBW for both interfaces as noted by Wayne.
The system will start up with both enabled, if you do that and your new ROM is buggy you'll blow stuff up, ditto in theory if a software glitch leaves both connected. I've got a dead 16GB SD card to show for that particular experience. It's not IMHO worth the risk given how trivial the fix is, although most folks only use/need one SPI device anyway.
Alan Cox
Aug 8, 2025, 7:15:17 AMAug 8
to retro-comp
If you are in the UK I've got spares of the SC126 mod PCB lying around somewhere so I can post you one.
Alan
To view this discussion visit https://groups.google.com/d/msgid/retro-comp/c1653b3e-9512-42d6-bffb-e2a70b22e200n%40googlegroups.com.
Fernando Carolo
Aug 8, 2025, 9:07:26 AMAug 8
to Alan Cox, retro-comp
And if you are somewhere in the EU I can send you a spare board, too.
--
Fernando
To view this discussion visit https://groups.google.com/d/msgid/retro-comp/CAK9X0%2Bs_u-P6S_rLX5gh8gCHwiXbKLW4YsNa4eg0-JrKcU99rw%40mail.gmail.com.
Timmy Austin
Aug 8, 2025, 12:29:34 PMAug 8
to retro-comp
You guys are both amazing. Thank you for the offer. I'm not in the EU or UK but I've already sent off for some boards and placed an order for the few parts that I didn't have to complete both boards (the SC720 and SC126). Now the painful part that I haven't figured out a way to deal with since childhood.....waiting, patiently. The poor wife knows I've ordered something because I have been wondering around looking under the couch and moving around the furniture in case it got delivered and it fell behind the TV!
Greg Holdren
Aug 8, 2025, 6:30:28 PMAug 8
to retro-comp
Yes, SW assisted HW. Port 0x0C could be dangerous if not written correctly. Most users are using released ROMs/code so the issue will be most likely minimal.
Greg
Timmy Austin
Aug 27, 2025, 10:43:07 PMAug 27
to retro-comp
Well it got here, it's all assembled and working great! A huge thank you to you, Mr. Cousins! Obviously, I thought I had a proper switch but didn't so that's on order. No worries though, I am currently powering via the FTDI to play around. Also, please don't judge my led placement there. It looked fine until I 3D printed the tray and now it is very obvious that I may have had too much adult juice that night!
So new noob question, if anyone is left.....I have never had a CP/M machine before. I was just young enough that I had to accept whatever was given to me and that was a commodore 64. Now I'm going on a little adventure to see everything I missed. I've read through the entirety of the CP/M manual and have noticed it's shortcomings (using today's glasses). I moved on to reading through the Z-system manual and tried booting into that from RomWBW. I notice that the DOS is different and DIR shows a slightly different format but nothing else much seems to have changed. I was most interested in the ability to name slices of the sd card and interact between say C3 and H11 as opposed to having to switch users. I was also interested in the 'path' ability to have 'native' apps that can be called from anywhere. Am I doing something wrong, or missing something? The RomWBW loader indicates that it is Z-system but it is lacking many of the built in fuctions like, say, ECHO or ALIAS. All of the same coms are available whether I choose CP/M or Z-System. I am sure that there is a very simple thing that I am misiing, I am just not sure what it is. I eventually intend to land that super high paying job as a Z80 assembly programmer but I need to learn the tools first and that has to start with the OS and file manipulation. Thanks for reading!
Mark Pruden
Aug 28, 2025, 8:38:29 AMAug 28
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Hi.
Quick Question: are you booting using the "Z" command, or booting from a disk drive by specifying its drive number ?
Quick Question: are you booting using the "Z" command, or booting from a disk drive by specifying its drive number ?
Just from the way you describe it, it sounds like you are doing the "Z" command. Problem is this isn't how its primarily meant to run. To get all the features you need to install and boot from an SD card. there is a whole section on how to do this in the RomWBW user guide, so I wont go into that.
* name slices of the sd card - is done via an app called SLABEL
* typing "C3:" will change to user area 3 on c: drive
* 'path' ability - when you boot from ZSDOS on SD card you should see assigned path's. Using "Z" you don't see this.
Mark.
Timmy Austin
Aug 28, 2025, 10:29:25 AMAug 28
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I am indeed booting using the Z command. It's on to the RomWBW manual for me now! lol. Thank you very much.
Matt Butch
Aug 30, 2025, 2:58:20 PMAug 30
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Wow thank you both! I too was looking through the plethora of options and having trouble deciding what I wanted to get. Both your thoughts and advice really helped me decide what I want to do!
On Wednesday, August 6, 2025 at 7:24:25 AM UTC-4 Steve Cousins wrote:
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