exxos's Atari, Amiga & retro forum

HigashiJun wrote: 10 Feb 2024 09:04

rubber_jonnie wrote: 10 Feb 2024 08:51 I don't, no. I don't feel compelled to get one either, at least not like some other machines.

Yeah, same here...

I cannot explain why, but I'm more attracted to some machines than others.

For me it is mostly about the machines that were about when I was young, starting with the ZX81 as my first computer. And a few other interesting ones...

8-)

OK, so it looks like I've misunderstood how the external cassette interface works. Thankfully a side conversation with @PhilC may have set me straight.

Going through the schematics the external input actually doesn't connect via the internal cassette, though it does go to the same 9 pin plug on the mainboard the internal cassette uses.

Phil suggested that he thought it might need to be jumpered in order to connect the external input, so I'm going to connect external cassette 'in' to the internal line on the same plug and see what happens.

Kind of kicks my assertion that the external in went through the amps in the internal cassette, it doesn't, and it is a lesson in paying attention to the schematics.

I had also originally thought that the cassette A/B switched between internal and external, but it doesn't, it just inverts the external cassette input waveform.

Will try jumpering it later and see what's what.

OK, so first jumpering attempt shows promise.

By connecting pin 2 of the 9 pin connector to pin 8, I am now seeing this signal:


The blue trace is the input at pin 8, and the yellow trace is at pin 12 of the 8255, so the signal is in fact arriving where it supposed to, and it also is a correct waveform and correct amplitude as expected at test point 6 of the cassette, however there is something else missing.

There is a sense line at pin 5 of the connector and it is connected to the read, write and motor circuits of the internal cassette, but I'm assuming it also requires a connection for the external cassette to work.

There is a switch that connects it directly to ground at some point but I haven't yet figured out when that comes into play, so more digging required.

It's also got some gates and an IC between it and the 8255, so I need to see just what sense does with the internal cassette running.

And as a bonus, here's the cat after he climbed into the bottom of my deskside drawers whilst I had the drawer open looking for cables...

So, the sense line is figured out, it just needs to be pulled to ground. What it does is tell the Sharp to listen for data as the tape is running. If that sense line is floating then it won't do a thing.

Essentially it's this switch here on the cassette deck:


Any time any key is pressed, so play, record, ffwd, rwd, this switch is made, pulling sense to ground. In fact the only time it isn't pressed is when the deck is stopped. So I connected pin 2 (ext read) to pin 8 (int read) and pin 1 (ext write) to pin 7 (Int write) so that the external inputs will work.

Since the sense line cannot be made when you execute the LOAD command (I don't know why, probably the sense input being out of order in the load sequence) I still required a switch in order for it to activate at the correct moment.

Well, it turns out that I have just that in the old internal cassette module. All I needed to do was do the ext to internal bodge wires underneath the mainboard, then connect up the old cassette unit and press play on that when I want to load from the external cassette interface.

EDIT: It turns out that LOAD does work at the monitor does load with the sense line connected to ground all the time, so I will likely return at a later date, disconnect the internal cassette completely and just tie pin 5 of the connector to ground permanently.

I verified this here: MZ-700 repairs.

So, does it work? Yes it does, here we can see it's loading Snake & Snake:


And the final result:


That's a result I'm happy with for sure.

Next thing I need to pull the keyboard apart, but will do that another day, as the cursor key cluster doesn't seem to be working, though everything else is.

I am going to see if I can find a replacement head for the internal cassette unit, and I need to see if I can find WAV files of the cassettes as so far Snake & Snake is all I can load!! So as yet no BASIC, but the tape does seem erratic during playback.

I will also try my other cassette deck to see if loading improves with that.

@rubber_jonnie there is usually a cheap as card solution on eBay for the sharp. I would have probably done it if I was keeping it.

Well done on getting it to load btw.

PhilC wrote: 11 Feb 2024 17:53 @rubber_jonnie there is usually a cheap as card solution on eBay for the sharp. I would have probably done it if I was keeping it.

Well done on getting it to load btw.

Yeah, I'm going to have a look and see what's out there for it :)

Just for funzies I tried to get another game to load, and it did!!!


I have to say, I kinda feel like the 2 games I've managed to load seem like they may have been created 'under the influence of substances.'

I dug out my USB cassette player which is the newest cassette player I have and it worked very well, so I may take the time to do a dump of all the cassettes I have just for the sake of archiving. We all know what cassettes are like...

It would also be interesting to see if my Acorn tape deck plays nicely with the Sharp.

Having done the whole 'bodge wire' thing earlier, now I know that the sense pin just needs to be tied to gnd, I may revisit and just make a removable jumper to go inside. We'll see.

Love the picture with your cat !

:D

HigashiJun wrote: 12 Feb 2024 01:22 Love the picture with your cat !

:D

:)