SC126 - available RAM/ROM

[shadow 338]

I just built a SC126 computer and I'm just loving it.

I have the following questions regarding available memory and mapping. (Please forgive if some may sound rookie questions or if they don't make much sense)

(as per the user guide)

"The Z180’s memory management unit deals with mapping chunks of this memory into the logical 64k memory map supported by the Z80/Z180 instruction set."

1- When booting RomWBW and then run '(M)onitor', when I try to dump memory above 0xFFFF I get an 'Syntax Error' which makes me wonder if the Monitor only supports 64K. The same happens under SCM (S6).

How we can access RAM above 0xFFFF from Monitor/SCM ?

2- When it's running BASIC (4.7b) under SCM it shows 32K of free RAM and 56K under RomWBW. Out of curiosity, does BASIC needs to be modified/compiled in order to be able to see more RAM? is 56k the very limit?

3- CP/M also shows around 53K of free RAM which makes me think that only 64K at a time are available. How memory paging can be performed? Is this only possible under CP/M?

4- On other computers (eg. RC2014 mini), we select the various ROM banks via jumpers. SC126 does not have jumpers for this so I guess to access/boot other parts of the ROM we need to add new boot entry under the 'SC126 Boot Loader'?

5- How about if I don't want to run RomWBW at all, from an HW perspective how memory banking works on SC126? My guess is that the SC126 was not designed for that purpose. (selectable rom banking)

Sorry for many questions and thank you!

H.

[Tadeusz Pycio]

The processor always has only 64kB of memory available. All available memory (e.g. 512kB) can be mapped to these 64kB via MMU, in Z180 they can be different areas (Common Aera 0, Common Aera 1 and Bank Aera) configured by CBR, BBR and CBAR registers. These areas can be dynamically changed programmatically. Access to "more" RAM is realized in CP/M 3 or MP/M II, but still it is available at the same time 64kB and switched memory banks

[Wayne Warthen]

Tadeusz basically answered this already, but I thought I would expand on the individual questions as best as I can.  See below.

-Wayne

On Friday, November 12, 2021 at 4:20:54 AM UTC-8 henrique...@gmail.com wrote:

1- When booting RomWBW and then run '(M)onitor', when I try to dump memory above 0xFFFF I get an 'Syntax Error' which makes me wonder if the Monitor only supports 64K. The same happens under SCM (S6).

How we can access RAM above 0xFFFF from Monitor/SCM ?

The "Syntax Error" message is correct because you can only dump memory that is in the current CPU address space.  Since the CPU address space ends at 0xFFFF, that is the highest you can enter.  Access to the full physical memory on a Z180 requires explicit programming to map different areas (banks) of memory into the CPU address space.

2- When it's running BASIC (4.7b) under SCM it shows 32K of free RAM and 56K under RomWBW. Out of curiosity, does BASIC needs to be modified/compiled in order to be able to see more RAM? is 56k the very limit?

I think the version of BASIC distributed with SCM is designed to work with all variants of SCM.  For some hardware, 32K of RAM is all that you get.  RomWBW requires hardware that provides a full 64K of RAM and so that version of BASIC can take advantage of more RAM.

3- CP/M also shows around 53K of free RAM which makes me think that only 64K at a time are available. How memory paging can be performed? Is this only possible under CP/M?

Yes, only 64K at a time.  On a Z180, you should read the Zilog manual to understand how physical memory areas are mapped into the CPU address space.

4- On other computers (eg. RC2014 mini), we select the various ROM banks via jumpers. SC126 does not have jumpers for this so I guess to access/boot other parts of the ROM we need to add new boot entry under the 'SC126 Boot Loader'?

ROM banks on the SC126 are selected in software, not hardware, so there are no jumpers.  Yes, if you want to add new tools to the RomWBW ROM, you also need to add new entries to the loader menu to get them loaded into the CPU address space.

5- How about if I don't want to run RomWBW at all, from an HW perspective how memory banking works on SC126? My guess is that the SC126 was not designed for that purpose. (selectable rom banking)

You can certainly do memory bank management without RomWBW.  I think you should review the Zilog Z180 documentation.

[shadow 338]

Thank you Tadeusz and Wayne, this is very useful information.