tynemouthsoftware.co.uk
Making new things for old computers.
http://blog.tynemouthsoftware.co.uk/
https://www.tindie.com/stores/tynemouth/
https://www.patreon.com/tynemouthsoftware
277 posts
1,039 followers
240 following
Regular Contributor
Active Commenter
comment in response to
post
I don't know how much matches the ZX80/81, but on there, port $FE (and all other even ports) read as
* D0-D4 are the keyboard columns
* D5 is not used
* D6 sets 525/625 lines
* D7 is ear input from the tape.
comment in response to
post
Is anything to do with the magic D6 on the ZX80/ZX81 ?
D6 has an extra pullup and a diode wired to the KBD signal (IORD with A0 low) in NTSC mode (so that bit reads 0). D11 is not fitted in PAL systems, so reads a 1 due to the pullup.
At least the heat will make desoldering easier.
comment in response to
post
You sometimes see RAM datasheets with alternate orders of address lines, but it doesn't really matter as data is read back from where it is written to.
It is nice to keep it "correct" to make fault finding easier, but sometimes the lines are shuffled around to make routing easier.
comment in response to
post
I'm still 10 away.
comment in response to
post
Nice work. I remember drawing something similar back in the day for my ZX81, but didn't have the skills to actually do it.
comment in response to
post
Interesting read, thanks for posting that.
comment in response to
post
I didn't have a double decker bus for scale, so here is a tin of beans.
(I didn't have a tin of beans either, but I am not sure the contents is critical)
comment in response to
post
The first couple of ZX81 controllers built on padboard used that. I was not happy with that approach, so switched to the microcontrollers with dedicated USB support.
comment in response to
post
comment in response to
post
Whilst I was sorting out relisting the Mini PET, I remembered this great video from Sam at Look Mum, No Computer.
www.youtube.com/watch?v=wCOF...
comment in response to
post
Meanwell + ATtiny45 was what I had to hand. Temporarily wired up, at some point I need to decide to do it properly and either locate a suitable plug housing and crimps or take the cable off the old power supply.
comment in response to
post
The signal from the power supply feeds a 50Hz or 60Hz signal to the TOD input on the CIA chip, which I think was needed for the keyboard scan interrupt, like the signal taken from the 9V AC on a C64.
In my temporary setup, I used an 8 pin microcontroller to supply that signal to get it booting.
comment in response to
post
My PSU is also in a bad way. Last time I was using a meanwell with a little microcontroller to generate the TOD pulse.
I would like to refurb the original, but I might just tidy up the replacement.
comment in response to
post
The PET microSD should work, but I don't think I have any of those left to be able to test.
I gave into to the "are you sure you don't have just one left?" a few too many times before the SD2PET was available.
The P500 is 1MHz, the interface is electrically identical and probably also the code.
comment in response to
post
I would have thought the 4040 "should just work".
I use an SD2PET with my P500, although I don't have much to load on it (and it's still got multiple RAM faults).
The SD2PET doesn't get on with the other 2MHz CBM II machines, but seems fine with the 1MHz P500.
comment in response to
post
As you can imagine, I have been testing an awful lot of ZX81 games on the Minstrel 4th.
It's a hard job, but someone has to do it.... :^)
comment in response to
post
I thought that said "Monkey Island Sauce", I think I would be more tempted by the adventure game flavoured version.
comment in response to
post
Could be. I have a couple of 8096SKs (one I got in 2013, one in 2016).
comment in response to
post
With various tweaks, I got the code short enough to make it run about 195% the speed of a ZX81.
I am writing a post about that separately.
I will be making that version available as an option, but I went with padding it out with a delay to slow it down to 100% speed as some games played too fast.
comment in response to
post
I thought I recognised my bench in that photo.
blog.tynemouthsoftware.co.uk/2018/10/tosh...
comment in response to
post
If you need a new Z80, I have some for sale on Tindie for $200. Comes with a few extra bits and pieces as well.
www.tindie.com/products/tyn...
comment in response to
post
Well spotted, thank you. Fixed. I usually try to leave one or two typos in, to make sure the readers are paying attention.
comment in response to
post
If you need a new Z80, I have some for sale on Tindie for $200. Comes with a few extra bits and pieces as well.
www.tindie.com/products/tyn...
comment in response to
post
LDI makes a big difference, thank you.