Talking of the 380Z...

Tony Duell ard at p850ug1.demon.co.uk
Sun Jul 3 13:17:53 CDT 2005


> 
> On Sat, 2005-07-02 at 23:10 +0100, Tony Duell wrote:
> > > I don't have any kind of docs for a tape-only system though; only ones
> > 
> > Nor do I. I've never actually seen a system without disk drives either, 
> > although I am pretty sure they existed.
> 
> We've got several 380Z's (well, two or three) that have no drives in
> them - I expect those are tape-only systems. Unfortunately I've never

Thay may have been used with external floppy units. The only way to be 
sure is to see what PCBs are inside.

> had time to look inside them as there's always been something more
> important to do! I know we've got one of the 8" drive setups too which
> are rather rare, plus we've got one 380Z-FD machine which should have
> the "full disk" controller in it (on-board RAM, ROM, its own Z80 cpu
> etc.).

I was readign the 380Z service manual on vt100.net this morning. It was 
the first time I'd come across this board, it looks rather fun.

I thought the 'full disk' controller was the 8" one (which was 
essentially the same as the normal 380Z controller), and that the one 
with the on-board Z80 was the Intellegent Disk Controller. But I could 
well be wrong.

> 
> (Said disk controller also has the SIO-4 on board, and the on-board

FWIW, the normal, non-intellegent disk controller has a SIO-4 on the same 
PCB, but it's nothing to do with the disk controller function. Obviously 
on that board you can go from serial port to disk without using the rest 
of the machine.

I believe the SIO-4 board (also SIO-5, SIO-6) was just a disk controller 
board with the serial chips fitted and the disk controller chips not 
fitted. Much as the RAM expansion board is the same PCB as the CPU board, 
but you leave off the CPU and buffers, etc.

> firmware should allow communication direct between the disks and the
> serial port - I believe it's the same board as used for the 480Z shared
> disk system)

That's what the service manual implied. I have a 480Z (one of the older 
metal-cased ones), but no disk unit for it.

> 
> What we don't have is keyboards. In some cases that's not such a big
> deal as with the later serial boards they could run from a terminal
> rather than system keyboard & display.

The keyboard interface spec is in the Information File and service 
manual. The latter also contains a scheamtic of  _a_ keyboard, but from 
what I rmemeber the one I have is very different. Not that said schematic 
is a lot of use for making one, since the contents of the microcontroller 
firmware ROM are not know. The keyboard I have (and from what I remember 
we had at school) has a single 40 pin custom chip in it, nothing more.

It would eb a fairly simple microcontroller project to make an interface 
from a PC keyboard (the old XT, AT, PS/2 ones) to the RML keyboard connector.

> > Pity. I'd hoped at least one original RML cassette esisted somewhere. 
> > >From reading the manual, it appers that the phase of the replay signal is 
> > critical (it was with some other tape interfaces too) and I was hoping I 
> > could get an original tape to set up against. Oh well....
> 
> Presumably saving some data on one (or more) tape-based system(s) would
> be enough to you to read it one yours and setup against that. Not as

No. What you need is the original (or known-to-be standard) cassette 
recorder. 

The point is that if the signal is inverted at any point, the system will 
not read high-speed (1200 baud) tapes reliably. I think it assumes a 
cycle starts with a rising edge, and if the signal is inverted, 
transistions between 1 and 0 bits on the tape and vice versa as seen by 
the system as odd-length cycles. This is explained (badly) in the 
information file.

Years ago I made an RS232-CUTS tape interface unit. It suffered from much 
the same problem, I included switches to invert the record and replay 
phase. I found that you could _not_ depend on cheap cassette recorded 
getting the phase right, or even being consistent between record and 
replay. In other words, to load a 'standard' tape (in my case I used a 
commercially-produced BasicCode tape), you would have to invert the 
replay signal with some recorders and not others. And once you'd got that 
right, you would have to invert the record signal with some recorders and 
not others to get it to record a tape that would load with the same 
setting as the BasicCode tape. 

In the xase of the 380Z, what I want to do is to try to load a real RML 
tape, sort out the replay phase using that, then sort out the recording 
phase so I can load my own recordings.

Oh well...

-tony




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