Search found 8947 matches

by hoglet
Tue Apr 07, 2020 9:03 am
Forum: acorn atom and system
Topic: Atom just acquired not working
Replies: 32
Views: 608

Re: Atom just acquired not working

Just to confirm what Roland is saying.... On my Atom: - BREAK pressed: 8255 pin 35 measures 3.79V to ground - BREAK released: 8255 pin 35 measues 0.15V to ground If I completely disconnect pin 35 by bending the pin out (to simulate a broken track), then it measure 0.00V, and the Atom still boots. Jo...
by hoglet
Mon Apr 06, 2020 7:20 pm
Forum: hardware
Topic: HELP! A3000 dead
Replies: 13
Views: 251

Re: HELP! A3000 dead

The routine for calculating a checksum of the ROM will make use of RAM, so a RAM fault could account for both of the first two items on the list. I could be wrong, but I don't think the ROM checksum does use RAM. There are plenty of 32-bit registers in the ARM, so there's no reason for it to need t...
by hoglet
Mon Apr 06, 2020 11:12 am
Forum: acorn atom and system
Topic: Atom just acquired not working
Replies: 32
Views: 608

Re: Atom just acquired not working

John, It's also worth just using a multimeter to confirm there is pin-pin connectivity on the relevant ICs. For example: - IC23 pin 14 to IC48 pin 5 - IC23 pin 15 to IC48 pin 4 - IC48 pin 6 to IC8 pin 1 - IC9 pin 6 to IC8 pin 2 - IC8 pin 3 to IC27 pin 1, IC28 pin 1 and IC29 pin 9 - IC49 pin 11 to IC...
by hoglet
Mon Apr 06, 2020 10:35 am
Forum: hardware
Topic: RGB to HDMI using a Pi Zero and a small CPLD
Replies: 995
Views: 57510

Re: RGB to HDMI using a Pi Zero and a small CPLD

Hey Dave, the source (first off) will be a an Australian Microbee. This, if you are not familiar with them, is a Z80 based and Australian made system which was sold in large numbers to Australian and Swedish schools. The "premium" iteration runs at 3.375MHz, has a pixel clock of 13.5MHz and the vid...
by hoglet
Mon Apr 06, 2020 9:56 am
Forum: hardware
Topic: RGB to HDMI using a Pi Zero and a small CPLD
Replies: 995
Views: 57510

Re: RGB to HDMI using a Pi Zero and a small CPLD

Hello Ingmar, I've just built a few of the latest version (6/8 bit) boards for myself and a couple of Canberra retro mates and the results out of the box on my BBC model B were outstanding. Thanks for all the effort that has gone into this project. You are most welcome - thanks for the positive feed...
by hoglet
Sun Apr 05, 2020 7:00 pm
Forum: hardware
Topic: MMC - Card? - Help needed.
Replies: 13
Views: 342

Re: MMC - Card? - Help needed.

Assuming Tricy tested the adapter when it was made, this is most likely: (1) A poor connection due to tarnished pins on the User Port socket. (2) A faulty 6522. (1) can be addressed by plugging/unplugging the connector about 20 times (2) can be diagnosed by swapping over the User and System 6522 chi...
by hoglet
Sun Apr 05, 2020 6:21 pm
Forum: acorn atom and system
Topic: Atom just acquired not working
Replies: 32
Views: 608

Re: Atom just acquired not working

I assume you have found an Atom schematic, and have some idea how the video RAM works. If not, you need to do a bit of research and ask more questions. When break is released, you would expect to see a burst of activity on NWDS and VGD as the screen in cleared. A logic probe would allow you to confi...
by hoglet
Sun Apr 05, 2020 1:04 pm
Forum: acorn atom and system
Topic: Atom just acquired not working
Replies: 32
Views: 608

Re: Atom just acquired not working

It seems the Video RAM writes are not happening, but everything else is fine. 1. the NWDS is not getting through to the video RAMs (it passes thrigh IC27). 2. the VDG signal is stuck high (inactive). This comes from IC8, which connects to IC23. You could try swapping IC27 and IC28 over. Or you could...
by hoglet
Sun Apr 05, 2020 12:20 pm
Forum: hardware
Topic: New SCSI Host Adaptor
Replies: 40
Views: 903

Re: New SCSI Host Adaptor

Ken,

Is there also some kind of termination at the far end of the SCSI bus, either on the drive or at the end of the cable?

(SCSI-1 is designed to have termination at both ends, because data can flow in either direction)

Dave
by hoglet
Sun Apr 05, 2020 11:40 am
Forum: hardware
Topic: New SCSI Host Adaptor
Replies: 40
Views: 903

Re: New SCSI Host Adaptor

Ken,

If you post the updated CPLD fitter report, I can check the logic equations for the open collector outputs look correct.

They should all follow this pattern:

Code: Select all

XXXX_I <= '0';
XXXX <= XXXX_I when XXXX_OE = '1' else 'Z';
XXXX_OE <= XXXX;
Dave
by hoglet
Sun Apr 05, 2020 11:28 am
Forum: hardware
Topic: New SCSI Host Adaptor
Replies: 40
Views: 903

Re: New SCSI Host Adaptor

I think this is already implemented in the code? // SCSI device databus bidirectional control wire [7:0] scsi_nDATA_in; wire [7:0] scsi_nDATA_out; // Here the input and output of the databus needs to be tied together // since the Acorn SCSI host adapter will drive the BBC databus output // latch fr...
by hoglet
Sun Apr 05, 2020 10:54 am
Forum: hardware
Topic: New SCSI Host Adaptor
Replies: 40
Views: 903

Re: New SCSI Host Adaptor

Baby steps: // assign scsi_nACK = ~scsi_ACK; assign scsi_nACK = (~scsi_ACK) ? 1'b0 : 1'bZ; // assign scsi_nSEL = ~scsi_SEL; assign scsi_nSEL = (~scsi_SEL) ? 1'b0 : 1'bZ; // assign scsi_nRST = bbc_nRST; assign scsi_nIRQ = (bbc_nRST) ? 1'b0 : 1'bZ; Does that look right? Not so sure about the databus....
by hoglet
Sun Apr 05, 2020 10:41 am
Forum: hardware
Topic: New SCSI Host Adaptor
Replies: 40
Views: 903

Re: New SCSI Host Adaptor

What is the current capability of the CPLD pins? You need 23mA sink (per pin) to drive SCSI-1 with a single terminator I think. Xilinx Application Note XAPP150 gives the I/V characterics for many of the Xilinx product families (derived I think from the IBIS simulation models): xc9500xl_v_i.PNG In m...
by hoglet
Sun Apr 05, 2020 10:17 am
Forum: hardware
Topic: New SCSI Host Adaptor
Replies: 40
Views: 903

Re: New SCSI Host Adaptor

I had another thought... The load on the SCSI data lines is quite significant, especially with the termination resistors at each end. When the CPLD is driving all the SCSI datalines and trying to pull them low, it's quite possible you are getting a significant spike of ground bounce that's upsetting...
by hoglet
Sun Apr 05, 2020 10:02 am
Forum: hardware
Topic: New SCSI Host Adaptor
Replies: 40
Views: 903

Re: New SCSI Host Adaptor

Hi Ken, In the original schematic , SEL, ACK and RST are driven by open-collector buffers. As is the data bus. This is, I think, how SCSI-1 was designed. When the driver is deactivated, the termination resistors return the signal to the high level in a controlled way. In your CPLD, they are driven b...
by hoglet
Sat Apr 04, 2020 9:41 pm
Forum: hardware
Topic: New SCSI Host Adaptor
Replies: 40
Views: 903

Re: New SCSI Host Adaptor

KenLowe wrote:
Sat Apr 04, 2020 9:26 pm
Circuit diagram attached.

Any words of wisdom?
How have you designed the CPLD?

Are happy you have correctly implemented the open collector outputs in the CPLD?

Dave
by hoglet
Sat Apr 04, 2020 12:52 pm
Forum: hardware
Topic: RGB to HDMI using a Pi Zero and a small CPLD
Replies: 995
Views: 57510

Re: RGB to HDMI using a Pi Zero and a small CPLD

Would it be possible to decode the output from the last 32 lines of MODE 4 on the Electron and transform it into text that filled the entire framebuffer, or doesn't the Pi have enough bandwidth for anything more than scanline conversion? I was thinking of transforming the last 1K of screen data int...
by hoglet
Fri Apr 03, 2020 2:02 pm
Forum: acorn atom and system
Topic: Atom tapes with non standard formats
Replies: 37
Views: 774

Re: Atom tapes with non standard formats

A bit more progress to report on the decoder.... I did try adding in the alternative byte decoder, and initially I thought it was getting better results, because fewer blocks were flagged as bad. But it turns out that quite a few of these so-called good blocks had two bit errors that cancelled each ...
by hoglet
Fri Apr 03, 2020 9:14 am
Forum: acorn atom and system
Topic: Bugs in Atom Basic
Replies: 2
Views: 119

Re: Bugs in Atom Basic

IanS wrote:
Fri Apr 03, 2020 9:09 am
Would you include this viewtopic.php?p=218802#p218802
Yes, I think so.
by hoglet
Fri Apr 03, 2020 8:26 am
Forum: acorn atom and system
Topic: Bugs in Atom Basic
Replies: 2
Views: 119

Bugs in Atom Basic

Hi all, This thread yesterday touched on a bug in Atom Basic if you use AA as an assembler label. This got me thinking about whether there are other bugs in Atom Basic. It would be interesting to try to compile a list. Does anyone know of any other bugs? I don't, so maybe it will be quite a short li...
by hoglet
Thu Apr 02, 2020 6:50 pm
Forum: acorn atom and system
Topic: Coding question
Replies: 14
Views: 360

Re: Coding question

Thanks so much , but not sure this will work since I don’t get an Out of Range message but an Error 156 , I don’t get an a chance to run the assembler code twice. Am I correct ? The two passes are still needed, but you are correct. I think the cause of your ERROR 156 is the use of AA as a label. I ...
by hoglet
Thu Apr 02, 2020 5:58 pm
Forum: acorn atom and system
Topic: Coding question
Replies: 14
Views: 360

Re: Coding question

You need to assemble the code twice.

Add a line 12:

Code: Select all

12 FOR I=0 TO 1
This must be just before the DIM P(-1).

And a line 185:

Code: Select all

185 NEXT I
That will allow the forward reference to AA2 to be properly resolved in the second pass.

Also, don't forget to add an RTS at the end!

Dave
by hoglet
Thu Apr 02, 2020 4:26 pm
Forum: acorn atom and system
Topic: Atom tapes with non standard formats
Replies: 37
Views: 774

Re: Atom tapes with non standard formats

Does anyone recognise this polynomial? I'm not an expert in these things, but working through the details, I think the polynomial is: X 8 + X 6 + X 5 + X 4 + X 2 + 1 (which is 01110101 or 0x75 in hex) As far as I can see, this doesn't match any of the standard 8-bit CRC polynomials listed here: htt...
by hoglet
Thu Apr 02, 2020 2:31 pm
Forum: acorn atom and system
Topic: Atom tapes with non standard formats
Replies: 37
Views: 774

Re: Atom tapes with non standard formats

For completion, the MJCOS tape format is as follows: <File Sequence> := <File> [ <File> ... ] <File> := <0.5s high tone> <Header Block> <Data Block> [ <Data Block> ... ] <Header Block> := Filename (upto 13 bytes, followed by 0x0D) File Flag (1 byte) Exec Address (2 butes) File number (1 byte) Start ...
by hoglet
Thu Apr 02, 2020 11:14 am
Forum: acorn atom and system
Topic: Atom tapes with non standard formats
Replies: 37
Views: 774

Re: Atom tapes with non standard formats

Yikes a half-cycle sounds tough to detect. But then, if you just have a nice steep filter for the high tone, do you get binary out quite cleanly? I haven't (yet) tried to record this onto tape, or read anything back. From this post, it seems Wim has some MJCOS tapes: https://stardot.org.uk/forums/v...
by hoglet
Thu Apr 02, 2020 10:55 am
Forum: acorn atom and system
Topic: Atom tapes with non standard formats
Replies: 37
Views: 774

Re: Atom tapes with non standard formats

I've just looked at MJCOS on a scope (PB7 of the 6522) and observed the following: - it supports 1200, 2400, 4800 and 9600 baud using imple FSK modulation - the high tone matches the baud rate, so at 1200 Baud this is 1.2KHz, at 9600 baud it is 9.6KHz - the low tone is half the frequency of the high...
by hoglet
Wed Apr 01, 2020 8:54 pm
Forum: acorn atom and system
Topic: Atom tapes with non standard formats
Replies: 37
Views: 774

Re: Atom tapes with non standard formats

janrinze wrote:
Wed Apr 01, 2020 8:53 pm
The wav file of the tape currently is 327.5 MB so a bit too big to handle as an attachment.
Could you possibly upload it to dropbox? It would be very useful to have the whole tape as a test case.
by hoglet
Wed Apr 01, 2020 7:04 pm
Forum: acorn atom and system
Topic: Atom tapes with non standard formats
Replies: 37
Views: 774

Re: Atom tapes with non standard formats

I've done a bit more work on this today. The program now takes a -b <baud> argument, with values 300, 600, 1200 and 2400. I've also refactored the byte decoders, so the frequency and cycles-per-bit are parameterized. This means I no longer have to special case each speed. I've tested it on a couple ...
by hoglet
Tue Mar 31, 2020 9:18 pm
Forum: hardware
Topic: RGB to HDMI using a Pi Zero and a small CPLD
Replies: 995
Views: 57510

Re: RGB to HDMI using a Pi Zero and a small CPLD

What are the models numbers of the two TVs you have tried?

Dave
by hoglet
Tue Mar 31, 2020 8:57 pm
Forum: acorn atom and system
Topic: Atom tapes with non standard formats
Replies: 37
Views: 774

Re: Atom tapes with non standard formats

This is the best I have done so far with ZARCH4. ZARCH 0000 c7 0100 2900 c2b2 95 true ZARCH 0001 f1 0100 2a00 c2b2 11 true ZARCH 0002 fc 0100 2b00 c2b2 6c true ZARCH 0003 ff 0100 2c00 c2b2 4d true ZARCH 0004 ff 0100 2d00 c2b2 1c true ZARCH 0005 ff 0100 2e00 c2b2 a6 true ZARCH 0006 ff 0100 2f00 c2b2 ...