Getting "CCCCC" (checksum) errors on all floppies

[Tim Halloran]

I'm new with the replica (but built it a few years ago). The replica seems to be working (basic and stuff) but when I try to use the SD card it mounts the disk but when I boot I get CCCCCCCCCC and so on. I believe this is checksum. I did look and the disk (I was trying CP/M floppy and Zork) is a floppy (not a hard disk). I used the SC Card Formatter and copied the disks. I just recently updated the software as described on the website.

Any suggestions?

[Chris Davis]

You're correct that the repeating "C" is a checksum error.  In the Altair-Duino it typically means there is a problem reading the SD card.  Are you able to read any floppy?

Was this ever working in the past?

[Tim Halloran]

On Monday, June 16, 2025 at 10:15:51 AM UTC-4 famousd...@gmail.com wrote:

You're correct that the repeating "C" is a checksum error.  In the Altair-Duino it typically means there is a problem reading the SD card.  Are you able to read any floppy?

Was this ever working in the past?

Great question, I'm not sure. I ran tests when I built it but could have overlooked the SD card.

* All the floppy loads *say* they loaded the disk then I get the checksum (C) error when trying to boot or use the disk. For example, going through https://adwaterandstir.com/2017/05/15/play-zork/ I get "[mounted disk ‘DISK08.DSK’ in drive 0]" but then "C"s when I set switch 3 and AUX1 down.

* List commands (like like the hard drive images) all fail. https://adwaterandstir.com/2017/10/02/mount-88-hdsk-hard-drive/ fails at step 2 (To get a list of Hard Disk images available: switch 13 up, switch 12 up, all other switches down.  Aux2 down will display directory of Hard Disk images.) with a hang.

This all suggests the SC is bad in some way (or the data path is bad). I'll open this up and take a look.  Does the "[mounted disk ‘DISK08.DSK’ in drive 0]" indicate it read the disk? or is that just a setup in memory?

[Chris Davis]

David would have to say for sure, but "mounted disk" simply means the Arduino code has made the disk available for reading, while the repeating "C" means CPM is not reading the disk.

What happens when you get a list of available disks (SW12 up, AUX2 down)?

[Marco]

It could be a good idea to check voltage on the SD card reader, and continuity between the Arduino and the reader. I recently wrote a post where I showed which SD reader pins should connect to where on the Arduino (and only there, solder bridges are not uncommon...): https://groups.google.com/g/altair-duino/c/vw17gymvDAo/m/f1C--Y4oBQAJ .

I assume the SD card is readable from your PC (probably, as you copied the files onto the SD card), and it is FAT32 formatted? Did you check another SC card?

Op maandag 16 juni 2025 om 17:49:30 UTC+2 schreef famousd...@gmail.com:

[Tim Halloran]

Thanks, super helpful!

Mystery solved, in fact the SD card never worked because it was not connected to the DUE (at all!). Failure to follow instructions several years ago :-) I'll fixt this up. Thanks so much for all the help.

[Marco]

Classic! :-D Good to hear it's fixed.

Op dinsdag 17 juni 2025 om 02:20:55 UTC+2 schreef hall...@gmail.com:

[Chris Davis]

That's literally the most common thing people miss building this.  I normally mention it first, but I forgot!

[Tim Halloran]

Fixed and working. Off to the underground empire.

[David Williams]

What a nice terminal. That's the one thing I've not been happy with. I either need to find a real vintage terminal, or make one of those 3D printed lookalikes.

On Tuesday, June 17, 2025 at 7:05:24 PM UTC-7 John Galt wrote:

remember to recharge your lantern batteries :-)

[Al L.]

We had the same issue with "CCCCCC" when trying to load from the SD card.  The solution was reformatting the SD card as FAT32 with default allocation size.  It seems that the SD card we received with our kit was formatted incorrectly (thought the data on it was correct).  Hope this helps someone.

AL