Recent posts

#1

Technical support - Hardware related / Re: CPC 6128 - white screen, b...

Last post by McArti0 - Today at 12:32

Test 74LS373 by spider hardware

#2

Emulators / Re: ACE for Linux,Mac, Windows...

Last post by roudoudou - Today at 11:55

Hi, some dev updates and an annoying bugfix...
http://www.roudoudou.com/ACE-DL/

Code Select Expand

- Bugfix FDC Head reload with ReadData (some residual code left...)
- Automatic time counters with Execution Breakpoints (min, max, current)
- HexFind and TextFind in Memory Explorer (press F and N to repeat)
- Text Edition in Memory Explorer + Text selection
- AY registers color change on modification
- FDC ReadTrack timings when Not Ready
- Snapshot default memory banking

text edition will still need some improvments in the future (a full keyboard mapping at least...)

#3

Technical support - Hardware related / Re: CPC 6128 - white screen, b...

Last post by McArti0 - Today at 11:37

no way of knowing if their test is running as expected or not and the results can't be trusted.

Test is Pin 24 z80 WAIT is permanent Lo after Step 3

#4

Technical support - Hardware related / Re: CPC 6128 - white screen, b...

Last post by McArti0 - Today at 11:01

@Bryce.
Notice that the clock inverter gets a heavy zero at the input - it has no chance of ticking even once. The freeze is sure and strong.On the address lines there is &B100 or &B101. I use rectifier diodes so they have a 60ns propagation time, they may not stop at the first LDIR address.

#5

M

Technical support - Hardware related / Re: CPC 6128 - white screen, b...

Last post by mmldrm - Today at 10:47

If the jumper wire is lying across the PCB and (as is the case here), the user doesn't have a scope to confirm the clock signal, then they have no way of knowing if their test is running as expected or not and the results can't be trusted.

I do have an oscilloscope now! And pin grabbers/clips should arrive today.

I know my kit was woefully inadequate initially (and still isn't ideal now) but hourly these will provide more reliable test results.

Thanks again for putting up with this situation.

#6

Technical support - Hardware related / Re: CPC 6128 - white screen, b...

Last post by Bryce - Today at 10:41

Just out of interest. Have you actually tried to do this setup in reality and confirmed it works? Or is this all based on theory?

I did exactly that yesterday. Everything I write in this thread is tested (on real CPC16128)

The reason I ask, is that connecting anything at all directly to a crystal pin will usually dis-balance the capacitance enough so that
the clock will either not start at all or will be unstable.

And that's how it should work. GA is supposed to permanently turn off the clock and thereby freeze itself in a specific state.

Well that's at least good to know. However, there's a reason why those capacitors and the 74 are extremely close to the crystal with very short traces. Just the additional capacitance and inductance of the extra wire is enough to disturb the clock. If the jumper wire is lying across the PCB and (as is the case here), the user doesn't have a scope to confirm the clock signal, then they have no way of knowing if their test is running as expected or not and the results can't be trusted.

Bryce. 

#7

Technical support - Hardware related / Re: cable DDI-1 for CPC 6128

Last post by SerErris - Today at 10:32

That is what I said:

Amstrad PIN 1-33 are signal pins, where shugart it is the even pins (2-34).

So we are talking about the same signal pins, that are never GND. At best they are NC.

Amstrad did just turned the connector arround, so that even will be odd and also that PIN 34 will become PIN 1 (READY)

Following that The Amstrad PINs 29,31 and 33 carrying +5V from diskdrive to power the controller (Amstrad Schematic) and that will convert to PINs, 2,4 and 6 on Shugart BUS.

As described above, all of those are signal pins and not connected to GND on shugart bus. Pin 2 and 4 are drive to interface pins, so there should be a pullup on the interface side (or on the drive side), but there is nothing driving the line from the interface to low and interface side should be on high impedance, so it should not be an issue. 
Pin6 however could be a driving pin with driver select 4. However on the CPC infrastructure, the DDI-1 does not use this line for anything (as well as DS3). 

In the Schematics of the 6128 Service manual, it looks like the cable would be connected to +5V...
You cannot view this attachment.

However looking at the board, they are really not connected.
You cannot view this attachment.

Anyhow, regardless if you connect it with cut lines or not, it will not harm the CPC (which we agree on :-) ).

#8

Technical support - Hardware related / Re: CPC 6128 - white screen, b...

Last post by McArti0 - Today at 10:32

Just out of interest. Have you actually tried to do this setup in reality and confirmed it works? Or is this all based on theory?

I did exactly that yesterday. Everything I write in this thread is tested (on real CPC16128)

The reason I ask, is that connecting anything at all directly to a crystal pin will usually dis-balance the capacitance enough so that
the clock will either not start at all or will be unstable.

And that's how it should work. GA is supposed to permanently turn off the clock and thereby freeze itself in a specific state.

#9

T

General Discussion - Introductions / Re: What computer did you have...

Last post by tronic - Today at 10:29

Nice topic.

On my side, my father realised that computers would change a lot of things. So in 1983 we bought a YENO SEGA SC3000.
This purchase (which was very expensive for the time) took a long time to mature after reading numerous magazines and comparing machines (and there were a lot of them... Far too many!) as well as numerous weekend visits to many computer shops.
I was 10 years old, with stars in my eyes, and I remember that delightful time as it was yesterday.

Of course, with hindsight, this machine was never viable (in France) but it had some very interesting and innovative technical features for its time (hard+zoom sprites, cartridge port...) and compared to other 'heavyweights'.
https://www.youtube.com/watch?v=i6MDryVo8UQ)

I discovered basic programming on this machine because the manual was particularly well written and full of examples. Also typed (and adapted, as they were often not compatible) a huge number of book and magazine listings. Joined a computer club dedicated to the machine, where my father and I would go at weekends to exchange tips. Bought peripherals (joystick, few -rare- games, a huge floppy disk drive that radically changed the situation compared with storage on k7, rs232c printer... etc).

When I started secondary school in 1984, the computer club had TO7, MO5 (a classic in France...) and an Apple IIe on which I also learnt a lot.
The CPC 464 came out that year, but few people had one, and at my level I found the machine visually horrible, with its green, blue and red keys...
I also already had a floppy disk drive for my YENO SC3000, so going back to k7 was nonsense.
The only advantage I could see was its monitor which would no longer take up a TV with a minimum of cables...

And then...
My neighbour (who had an Alice from Matra-Hachette, a tasteless machine...) finally bought a CPC 464 on which we spent whole days playing games, typing up listings, like many of us.
The maths teacher who ran the school computer club also bought a 464 and swore by it !
And so did many of my classmates and teachers...
The Amstrad software library was exploding, and so were the peripherals...
The French press had nothing but praise for this machine...
The 664 appeared, briefly... But it was when the 6128 came out, with its less 'playschool' look, that the machine finally arrived at home for Xmas, as I imagine it did for many of you.

Already a fan of computer clubs and other 'technological' weekend outings, the first (or second, can't remember...) amstrad expo in France with my father left me with delicious memories, despite the noise and the infernal crowds!
The following ones, where I went this time with friends from secondary school and over several days, were extraordinary. It was at this point that I gave up basic, copying games and started programming in z80 assembler...

What a wonderful time...

Tronic/GPA.

#10

Technical support - Hardware related / Re: CPC 6128 - white screen, b...

Last post by Bryce - Today at 10:25

How to test 74LS373 without desoldering.

The pictures show the procedure for stopping CPC on a single read from the internal RAM memory. at the end we have the state of open 74LS373. RAMRD and READY are low.

ORG #0638
LD HL,#B100
LD DE,#B101
LD BC,#07F9
LD (HL),A
.L0642
LDIR    <----- here we are stoping CPC

By setting the data pins of the internal bus, you can check whether these states pass to the external bus side. RAM pin 14 set to Lo (grounded) should show the same on pin 2.

If you are surprised by the polarization of diodes, know that I am surprised too.

Just out of interest. Have you actually tried to do this setup in reality and confirmed it works? Or is this all based on theory?

The reason I ask, is that connecting anything at all directly to a crystal pin will usually dis-balance the capacitance enough so that
the clock will either not start at all or will be unstable.

Bryce.