Search found 337 matches

by Nasta
Fri Oct 11, 2019 11:37 pm
Forum: Hardware
Topic: DIY QubIDE Parts list
Replies: 15
Views: 779

Re: DIY QubIDE Parts list

top.jpg bottom.jpg Note red arrows. There are a couple of different problems, when you can see the outline of the PCB pad around the solder, it's likely a bad/cold solder joint/ There are also a few pins on the SIL resistor pack where the surrounding ground fill has been exposed, and it's possible ...
by Nasta
Thu Oct 10, 2019 10:06 am
Forum: Hardware
Topic: Microdrive spinning ad infinitum...
Replies: 30
Views: 846

Re: Microdrive spinning ad infinitum...

The inductors on the switching regulator produce a rather large stray field which is probably being induced directly into the head and electronics. Even on the original QL the left microdrive has a metal shield between it and the motherboard stuff and in that setup there is FAR less electromagnetic ...
by Nasta
Tue Oct 08, 2019 10:19 pm
Forum: Hardware
Topic: Microdrive spinning ad infinitum...
Replies: 30
Views: 846

Re: Microdrive spinning ad infinitum...

Check that the 8302 ULA is well and alive. This sounds like either an interrupt is left 'hanging' or the MDV select signal or some other logic is - in either case, it's the 8302 that generates those control signals. Reversing the 5V polarity is REALLY dangerous and can easily damage any chip in the ...
by Nasta
Tue Oct 08, 2019 10:13 pm
Forum: Hardware
Topic: DIY QubIDE Parts list
Replies: 15
Views: 779

Re: DIY QubIDE Parts list

Someone else may know if this should work? (I'm not familiar with this board, or it's circuit diagram) If you remove all the plug-in IC's ( it looks like the two SMD IC's have something to do with the IDE socket), and plug it in. Does the QL work normally, or do you still get the bars? If you do th...
by Nasta
Tue Oct 01, 2019 8:20 am
Forum: Hardware
Topic: DIY Fpu Unit for STFM
Replies: 28
Views: 3200

Re: DIY Fpu Unit for STFM

Hi, Cannot help thinking more about $Fxxx and $Axxx. The emulation can be achieved through exception trap vectors. As on plain MC68000/8 $Fxxx and $Axxx machine code instructions simply do not exist. So the attempt excecuting them leads to an exception that can be caught by a handler. The respectiv...
by Nasta
Tue Sep 10, 2019 2:11 am
Forum: Hardware
Topic: DIY Fpu Unit for STFM
Replies: 28
Views: 3200

Re: 74HCxx vs 74LSxx

Shouldn't be a problem, the 68k CPU does not dissipate that much heat so hat being partially occluded by a ribbon cable would be a big problem.
by Nasta
Thu Aug 15, 2019 3:01 pm
Forum: Hardware
Topic: Mod on ULA
Replies: 9
Views: 991

Re: Mod on ULA

"These aren't the microdrives [droids] you're looking for". These are not the signals you are looking for :) Quite literally, I think the problem is the MDV circuitry generates spurious interrupts. To be honest, I'd be tempted to keep the machine just to show other people it had gesture r...
by Nasta
Wed Aug 14, 2019 4:54 pm
Forum: Hardware
Topic: Issue 8 discussions...
Replies: 125
Views: 13046

Re: Issue 8 discussions...

The 8302 does not have any significant impact on the speed of the whole machine as it's usually accessed in short bursts and, compared to RAM, infrequently. That being said, several pieces of code that access various parts of the 8302 are quite timing critical. Having the 8302 connected to the RAM b...
by Nasta
Tue Aug 13, 2019 12:11 pm
Forum: Hardware
Topic: DIY Fpu Unit for STFM
Replies: 28
Views: 3200

Re: 74HCxx vs 74LSxx

Interesting that no-one mentioned the biggest difference between HC and LS - power requirements. HC(T) uses power practically only when the signal transitions or there is a resistive load, the latter not being the case when it only drives other HC(T) or CMOS and indeed NMOS circuits like CPU or FPU ...
by Nasta
Sun Aug 11, 2019 12:19 pm
Forum: Hardware
Topic: Mod on ULA
Replies: 9
Views: 991

Re: Mod on ULA

The 2 resistors connect to -12v supply and each resistor is in turn connected to the raw data inputs to the ULA from the Microdrive. Some kind of negative bias to better address the input threshold switching maybe ? Some time ago I've been told the RAW lines mean Read And Write. When the MDVs are n...