Search found 1194 matches

by dp11
Wed Sep 16, 2020 11:47 pm
Forum: 8-bit acorn hardware
Topic: New SCSI Host Adaptor
Replies: 106
Views: 4736

Re: New SCSI Host Adaptor

Remember 74hct245 can't drive 24mA so won't work.
by dp11
Wed Sep 16, 2020 10:34 pm
Forum: 8-bit acorn hardware
Topic: Help! Master 128 Resurrection (hopefully)
Replies: 15
Views: 542

Re: Help! Master 128 Resurrection (hopefully)

You do can try a 74LS04 but it might not work, you should really should use 74S04
by dp11
Wed Sep 16, 2020 10:29 pm
Forum: 8-bit acorn hardware
Topic: New SCSI Host Adaptor
Replies: 106
Views: 4736

Re: New SCSI Host Adaptor

SCSI Bus is designed to be driven with an open collector drive. The terminator is designed to terminate the bus at typically 2.85v. One of the reasons for open collector is if multiple devices are on the bus with the same IDs there won't be a bus conflict. Input levels need to be : Vih >2v , ViL<0.8...
by dp11
Wed Sep 16, 2020 8:05 am
Forum: 8-bit acorn hardware
Topic: Pi-based Co-Pro on the cheap - 100MHz 6502 for £10? (now 290MHz)
Replies: 1264
Views: 159048

Re: Pi-based Co-Pro on the cheap - 100MHz 6502 for £10? (now 290MHz)

The cores written in c show the greatest performance increase with the Pi4 e.g lib6502
by dp11
Tue Sep 15, 2020 10:00 pm
Forum: 8-bit acorn hardware
Topic: Pi-based Co-Pro on the cheap - 100MHz 6502 for £10? (now 290MHz)
Replies: 1264
Views: 159048

Re: Pi-based Co-Pro on the cheap - 100MHz 6502 for £10? (now 290MHz)

As the extra memory isn't used, the Pi4 can just be the cheapest ( 2Gbytes @ £35) Also some people have over clocked the Pi4 for extra performance
by dp11
Tue Sep 15, 2020 11:33 am
Forum: 8-bit acorn hardware
Topic: Help! Master 128 Resurrection (hopefully)
Replies: 15
Views: 542

Re: Help! Master 128 Resurrection (hopefully)

just spotted it looks like the scope has a 20MHz bandwidth limit filter now on channel 1 can you turn that off.
by dp11
Tue Sep 15, 2020 11:32 am
Forum: 8-bit acorn hardware
Topic: Help! Master 128 Resurrection (hopefully)
Replies: 15
Views: 542

Re: Help! Master 128 Resurrection (hopefully)

Excellent now try probing pin 2 . If that doesn't give you a signal and there is no obvious signs of damage I think you need a new 74S04 .
by dp11
Mon Sep 14, 2020 2:15 pm
Forum: 8-bit acorn hardware
Topic: Help! Master 128 Resurrection (hopefully)
Replies: 15
Views: 542

Re: Help! Master 128 Resurrection (hopefully)

Excellent can you now go back and look at the clock pins now the scope is setup in a suitable way
by dp11
Mon Sep 14, 2020 2:35 am
Forum: 8-bit acorn hardware
Topic: Help! Master 128 Resurrection (hopefully)
Replies: 15
Views: 542

Re: Help! Master 128 Resurrection (hopefully)

I'd like to see how the scope displays it. The scope probes should be set to X10. I don't know how the scope does its vertical maths. But what you want is to adjust the the vertical gain and positioning of the trace to be say 5 divisions different from nothing connected to the probe tip. The go back...
by dp11
Sun Sep 13, 2020 7:22 pm
Forum: 8-bit acorn hardware
Topic: Help! Master 128 Resurrection (hopefully)
Replies: 15
Views: 542

Re: Help! Master 128 Resurrection (hopefully)

Can i have a scope trace of pin 14 too the 5v pin.

To see the clocks the time base needs to be be some like 0.1us per division.
by dp11
Tue Sep 08, 2020 2:40 pm
Forum: 8-bit acorn hardware
Topic: Help! Master 128 Resurrection (hopefully)
Replies: 15
Views: 542

Re: Help! Master 128 Resurrection (hopefully)

Can you post a picture of your scope showing nothing?
by dp11
Mon Sep 07, 2020 7:40 pm
Forum: 8-bit acorn hardware
Topic: Help! Master 128 Resurrection (hopefully)
Replies: 15
Views: 542

Re: Help! Master 128 Resurrection (hopefully)

Firstly are you an experienced scope user ?

What do you see at pin1 and Pin 13 of IC43
by dp11
Thu Sep 03, 2020 11:17 pm
Forum: 8-bit acorn hardware
Topic: Wobbly Clock
Replies: 9
Views: 373

Re: Wobbly Clock

Set the trigger position to the middle of the screen instead of a 22mS delay will also help. Also make sure the ground lead of the scope is very short ( don't use the ground lead that come with the scope) and is connected to IC43 pin7 if you really want to measure the clock accurately.
by dp11
Sat Aug 29, 2020 7:34 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 434
Views: 12060

Re: 8271 disc controller craziness -- do not try this at home!

Gray code address makes jumps hard and jumps can have all bits changing so don't actually buy you anything.
by dp11
Wed Aug 26, 2020 2:06 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 434
Views: 12060

Re: 8271 disc controller craziness -- do not try this at home!

Coeus wrote:
Wed Aug 26, 2020 1:31 pm
Ok, so this should be correct, then:
Looks good to me.
by dp11
Wed Aug 26, 2020 12:28 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 434
Views: 12060

Re: 8271 disc controller craziness -- do not try this at home!

As I have said before the pad below vcc is a pin that doesn't come out of the package. So you are off by one. GND is also a give away being on the right of the die images.
by dp11
Sun Aug 23, 2020 6:03 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 434
Views: 12060

Re: 8271 disc controller craziness -- do not try this at home!

Could be I wonder if a few of the address bits are a cycle counter.
by dp11
Sun Aug 23, 2020 12:34 pm
Forum: 8-bit acorn hardware
Topic: VIDPROC V2 (pin 15) - please explain!
Replies: 33
Views: 854

Re: VIDPROC V2 (pin 15) - please explain!

Some scope traces form an Issue7 mother board with VTI ULA

IC40 Pin13
Pin13.png
IC40 Pin12
ULAPin8.png
IC40 Pin11
Pin11.png

ULA Pin8
Pin12.png
ULA Pin15
ULAPin15.png
by dp11
Sat Aug 22, 2020 5:47 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 434
Views: 12060

Re: 8271 disc controller craziness -- do not try this at home!

The white/grey trace has a reasonable chance of being D0
by dp11
Fri Aug 21, 2020 8:48 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 434
Views: 12060

Re: 8271 disc controller craziness -- do not try this at home!

It looks like an input only pad so it could enable some sort of test mode.
by dp11
Fri Aug 21, 2020 8:35 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 434
Views: 12060

Re: 8271 disc controller craziness -- do not try this at home!

I've just been comparing the pinout with the datasheet . I think the spare pin is the one on the left just below VCC
by dp11
Fri Aug 21, 2020 7:58 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 434
Views: 12060

Re: 8271 disc controller craziness -- do not try this at home!

A0 A1 do come from the outside world , but I don't understand why they would go into a structure like the databus does .
by dp11
Fri Aug 21, 2020 5:19 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 434
Views: 12060

Re: 8271 disc controller craziness -- do not try this at home!

I think GND and VCC are swapped the Databus I think is bottom right as it has bigger transistors than standard IO pins according to the datasheet . You also get a better fit between Input only pins and Output pins.
by dp11
Fri Aug 21, 2020 11:57 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 434
Views: 12060

Re: 8271 disc controller craziness -- do not try this at home!

Anyone go any good ways of us group working on identifying bits of this chip ?

The data sheet says it has a 16bit CRC generator. I haven't yet spotted a 16bit structure.

Thanks

Dominic
by dp11
Thu Aug 20, 2020 11:12 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 434
Views: 12060

Re: 8271 disc controller craziness -- do not try this at home!

My guess in right hand side power pad in GND with the data bus going down and around the corner
by dp11
Thu Aug 20, 2020 10:42 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 434
Views: 12060

Re: 8271 disc controller craziness -- do not try this at home!

have we actually got two different controllers ? one at the top and one at the bottom ?
by dp11
Thu Aug 20, 2020 10:40 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 434
Views: 12060

Re: 8271 disc controller craziness -- do not try this at home!

I wonder if the 10 bit structure is either a timer or divider ?
by dp11
Thu Aug 20, 2020 10:26 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 434
Views: 12060

Re: 8271 disc controller craziness -- do not try this at home!

bottom left looks like 256 bytes of ROM.

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