Isami Guy SC126

[Mark Pruden]

I just saw the you tuber ISAMI Guy publish a couple of videos featuring the SC126

https://www.youtube.com/watch?v=vcN16_Zz_MY

[Steve Cousins]

I noticed an uptick in orders for SC126 and went looking for the reason. It appears the IMSAI Guy is the reason.

[John O'Brien]

Lol... I watched his 126 video and I love an SBC, I've built the N8VEM SBC and a few others... I thought "ooo... I need one of these!" Then realized I have the SC131, Lol

--
You received this message because you are subscribed to the Google Groups "RC2014-Z80" group.
To unsubscribe from this group and stop receiving emails from it, send an email to rc2014-z80+...@googlegroups.com.
To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/06b15a20-fec2-4b58-b1e8-16e82b88598en%40googlegroups.com.

[Michelle Lawson]

Well, frankly Steve, it does look like a really interesting project. I just don't know enough about the Z-80180 quite yet; like is the memory linear/contiguous, or is it just internally bank switched, still with a 64K direct limit?

[grahamebenson28]

I bought one of these about 5 years ago, a great bit of kit

Sent from my Galaxy

--

[Alan Cox]

On Sun, 7 Dec 2025 at 16:18, Michelle Lawson <michelle...@gmail.com> wrote:

Well, frankly Steve, it does look like a really interesting project. I just don't know enough about the Z-80180 quite yet; like is the memory linear/contiguous, or is it just internally bank switched, still with a 64K direct limit?

eZ80 is the first with a 24bit mode. 64180/Z180 instead has a fairly basic external memory manager that lets you partition the memory up a little bit. More than sufficient for things like banked CP/M and there were professional tools that knew how to give the impression of 56K data/stack and unlimited C code space by playing games with the memory manager.

Runs ROMWBW and other stuff very nicely. It's also fairly easy to add internet and CP/NET support with a WizNET 5500 (does need a small expansion board to use multiple SPI devices at once safely but you can always use CF for disk which is faster than SD card anyway). With CP/NET it's really nice as you can run a CP/NET server on a Linux box and have a shared drive between Linux and the board when developing stuff.

EmulatorKit has a simulator for the standard SC126 config if you want to play with it in emulation first.

Alan

[Steve Cousins]

Hi Michelle

Yes, it is still has the Z80's 16-bit direct address register limitations. However, it includes a memory management unit supporting 1MB of physical memory space. The MMU allows parts of the physical memory to paged into the 16-bit address range. So, in terms of memory, it is rather like the RC2014 Z80 CPU module plus an RC2014 1MB (512+512) memory module.

The Z8S180 CPU also includes two asynchronous serial ports, a clocked serial port, interrupt controller, two timers, and two DMA channels. As a result of all these built in features it is relatively easy to build a sophisticated 8-bit system with far fewer components than a system based on a Z80 CPU.

Have a look at SC722 and SC721 for a modular Z180 system which can work with many RC2014 compatible modules.

As always with retro systems: How retro do you want it?

Steve

[Michelle Lawson]

I kinda figured that was the case. That said, I'd love to learn of a chip that would run Z-80 code out of the box, and run CP/M at the top of a 1MB address space, so I had way more than 60K+ of directly addressable memory. I love the Z-80, always have, always will; I just want more direct memory.... oh well

[Bill McMullen]

"...run CP/M at the top of a 1MB address space, so I had way more than 60K+ of directly addressable memory"

Obviously the basic Z80 and it's instruction set will not allow 1MB of directly addressable memory without extra HW.  I've configured the Z180 to have CP/M in the uppermost 64K (i.e. F,xxxxh) on several of my designs with 1MB RAM.  I also have several eZ80 designs with 512KB-4MB of RAM where I happen to place CP/M 2.2 at 20,0000h+ but that could easily be changed to something like 3F,0000h-3F,FFFFh.  Both the Z180 & eZ80 run the basic Z80 instruction set with added new instructions and I've had no compatibility issues with standard CP/M applications.

FYI: There are those who believe that Z80 instructions "LD B,B : LD C,C : LD D,D : LD E,E" should have been retained on the eZ80 even though they're exactly the same as a NOP and were re-purposed as prefixes.  Personally, I believe a NOP is much more descriptive and I refuse to use self-modifying code which would be the only possible reason for their retention.

[Mark Pruden]

> run CP/M at the top of a 1MB address space, so I had way more than 60K+ of directly addressable memory. 

It is possible to address additional RAM banks in modern RomWBW, its an out of the box feature. A RAM disk drive occupies about half the banks, some are reserved for CpM, but several are left for user programs. 

But it requires programs to be adapted to take advantage. Of note I think the HiTech C compiler (modern version) has been adapted to support this providing significant benefits. 

[ladislau szilagyi]

Hi Mark, 

Yes, you're right, I customized the HiTech C compiler to use these additional RAM banks under RomWBW ( see https://github.com/Laci1953/HiTech-C-compiler-enhanced/tree/main/Executables%20for%20RomWBW ).

And, indeed, the benefits are significant (e.g. compiling the  Colossal Cave adventure game, as a single C file of 3700 lines)

Ladislau

[Mx Argent]

Small world! I just got an order in for one as a way to introducing myself to the Z180 and easing my way back into RCBUS/ROMWBW country after experimenting with other hobbyist busses for a few years. Not related to the video; mine was a late birthday gift.