New Zealand Vintage Computer Forums

I've been having fun with a FreHD.
http://www.classic-computers.org.nz/blo ... model4.htm

Nice writeup Terry.

I do have a bit of a passion for the FreHD having been involved in the project for a long time but it really is a fabulous accessory for the TRS80 series machines thanks to the hard work from a dedicated group of developers.

Because it emulates the WD1010 Hard Disk controller it is a viable option for other machines that used a WD1002 or WD1010 controller as the Kaypro project shows.

The hardware integration is generally simple and it is the software side that takes some work.

If I ever find some S-100 boards I want to build up a CP/M machine that uses a FreHD for storage. I am sure writing a CBIOS for CP/M is an important skill to have in 2014!

TRS80 wrote:If I ever find some S-100 boards I want to build up a CP/M machine that uses a FreHD for storage. I am sure writing a CBIOS for CP/M is an important skill to have in 2014!

LOL, Well it certainly would be a rare skill

Have you thought of adapting something from the N8VEM project to build a "modern" FreHD enabled CP/M machine from scratch. Or do you want to use old S-100 hardware?

LOL, Well it certainly would be a rare skill

It may not be as rare as you think.

I have build a number of single board Z80 machines including Grant Searle's excellent design (http://searle.hostei.com/grant/cpm/index.html) and done some work with Grant to get IOByte support into the BIOS. There are some writeups on this at http://www.quicktrip.co.nz/jaqblog/home/62-z80part1... and a few other pages. I probably need to organize the blog better.

A bit of an enthusiast for the Z80 really and while CP/M is pretty basic I do quite enjoy hacking around on it.

I have the N8VEM "Home Computer" PCB waiting to be built but these and most of my other Z80 machines really represent the later stage of the Z80 era so I am really keen to find an early S-100 bus system (or parts) as a restoration project. There are "new build" Z80 PCB's available from time to time through N8VEM but modern isn't quite the same even if it is better and more reliable.

TRS80 wrote:There are "new build" Z80 PCB's available from time to time through N8VEM but modern isn't quite the same even if it is better and more reliable.

Yes, I completely understand.

Andrew do you know much about the CP/M modification that could be done on the System 80 in the day? The hardware mod details and the details of the disk format that was used? Do you have any docs?

On the System 80 site I have rough docs of a John Gilbert 64k upgrade, but I'm not sure that's the same thing as a CP/M mod. Were the disks written in a format similar to the Kaypro for example? Or Model 4 CP/M ( Montezuma Micro)? Do you know?

Some time in the future it would be fun to Mod one of my System 80 for CP/M.

tezza wrote:

TRS80 wrote:There are "new build" Z80 PCB's available from time to time through N8VEM but modern isn't quite the same even if it is better and more reliable.

Andrew do you know much about the CP/M modification that could be done on the System 80 in the day? The hardware mod details and the details of the disk format that was used? Do you have any docs?

On the System 80 site I have rough docs of a John Gilbert 64k upgrade, but I'm not sure that's the same thing as a CP/M mod. Were the disks written in a format similar to the Kaypro for example? Or Model 4 CP/M ( Montezuma Micro)? Do you know?

Some time in the future it would be fun to Mod one of my System 80 for CP/M.

The difficulty with CP/M on the Model I,III and System 80 is the memory map of the machines. CP/M expects the low memory to be RAM and applications load starting at address 0x0100. On these machines this is ROM. Add to that the IO devices (screen, keyboard, printer, etc) mapped into the 0x37xx memory block and you have machines that will not run CP/M without modification.

Generally this modification is a board that fits into the Z80 socket and changes the address map. The Omikron Mapper is one such board for the Model 1. I don't think the John Gilbert modification does the remapping but I will look at it closer.

Once you have the hardware sorted then you need a boot rom that knows how to read the CP/M operating system from the disk. The Omikron Mapper had this on board and gave the option of CP/M or TRS-80 mode on boot.

I have Ian's newsletter DVD so will have a look and see if there are any CP/M mods documented there. Aside from the hardware, finding a copy of the boot disk will be important.

While the same applications will generally run on all CP/M machines the operating system itself won't without a BIOS configured for the specific hardware. This means finding a documented hardware modification is part of the job. You also need to find a boot disk with a BIOS compatible with the modifications. While most of CP/M is device independant the BIOS is specific to the hardware.

This "device independance" resulting from having device specific code in the BIOS seperate from the rest of the OS was one of the ground breaking concepts CP/M introduced and is why it was available across such a variety of machines.

The little Compuspec Z80 board I wrote about handles the ROM/RAM issue in a neat way. When it boots it copies the ROM (which starts at 0x000 like the TRS-80) into RAM starting at the same address and then disables the ROM. Grant Searle's 9 chip CP/M does something similar by disabling the ROM in the CP/M boot loader.

Here you are Terry.... http://www.quicktrip.co.nz/jaqblog/files/SydtrugVol5_9.pdf

Page 8 has an article on the hardware conversion for a System/80 to swap the upper and lower 16K blocks so the machine can run CP/M.

Thanks for that.

Terry.... your FreHD post prompted me to get back to the blog http://www.quicktrip.co.nz/jaqblog and do a little writeup on the FreHD installations for my Model 4 and 4P.

Having a few old hard drive frames in the junk box is an enabler for this type of project.

Nice,

Nice photos and good writeup Andrew. The use of a hard disk case is a great idea. It looks very tidy.