Search found 332 matches

by Nasta
Tue Sep 10, 2019 2:11 am
Forum: Hardware
Topic: 74HCxx vs 74LSxx
Replies: 15
Views: 2186

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: 902

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: 12071

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: 74HCxx vs 74LSxx
Replies: 15
Views: 2186

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: 902

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...
by Nasta
Sat Aug 03, 2019 7:14 pm
Forum: Hardware
Topic: Issue 8 discussions...
Replies: 125
Views: 12071

Re: Issue 8 discussions...

Well, the schematic has more or less been fixed for a while. One thing that has been done is that the original video RAM (first 64k) has been replaced by real dual port RAM, which uncouples CPU and video accesses completely, there is never any contention or slowdown. This also makes it possible to a...
by Nasta
Fri Aug 02, 2019 8:57 pm
Forum: Hardware
Topic: Issue 8 discussions...
Replies: 125
Views: 12071

Re: Issue 8 discussions...

Not silent, just very busy until Oct. 1st - yesterday. Lots of deadlines before most suppliers go to collective holidays.
by Nasta
Mon Jul 29, 2019 12:42 am
Forum: Software & Programming
Topic: A programming question
Replies: 6
Views: 705

Re: A programming question

It seems RAM is limited by compatibility with one of the superbasic compilers (Qliberator?) which used the top 3 bits of the address references to store data about the reference. These need to be 'don't care' for decoding (which also makes it 'fun' to write cache management code...), so only bits 28...
by Nasta
Wed Jun 26, 2019 9:33 am
Forum: Software & Programming
Topic: Hardware pointers and cursors.
Replies: 30
Views: 2476

Re: Hardware pointers and cursors.

I've never used the PE for longer than it takes to disable it. In that brief time I have observed that it displays a no entry symbol of red on white, and a pointer of two colours, and sometimes a question mark of two colours. I have never been exposed to how they are internally formatted. Even the ...
by Nasta
Wed Jun 26, 2019 2:24 am
Forum: Software & Programming
Topic: Hardware pointers and cursors.
Replies: 30
Views: 2476

Re: Hardware pointers and cursors.

To make a long story short, the gain in responsiveness will be disappointingly small if at all observable. And it will come at considerable complication to drivers, because under PE the cursor can be more than a 2-bit deep bitmap with the given hardware limitations. The OS updates the cursor under ...