Altair 8800 Simulator and disks on SD card

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Antonio Tamairón

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Jan 23, 2026, 11:35:08 AM (5 days ago) Jan 23
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Hi.
I recently assembled the Altair 8800 simulator by David Hansel is a beatiful project.
I have a problems when I try to boot programs from SD card.

I have installed SD card interface on Arduino Due according to the documentation. The simulator is connected to terminal serial though serial port 18/19 pinout.

I follow the steps for example to load Microsoft Basic (according to the documentation) summarizing

1. Mount disk on driver 0 - Message appear about mount is ok
2. Now launch "boot loader ROM"
3. The screen is filled with a "C" character

Chris Davis

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Jan 23, 2026, 11:53:51 AM (5 days ago) Jan 23
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From your post, I'm assuming you sourced the parts and assembled this from scratch and not from the kit?

That is a checksum error.  There is possibly something wrong with the way you have connected the SD card.  Are you using an SD card module, or do you have the leads soldered directly to the SD card?

When you raise RESET and AUX1, does your configuration menu show "File System Manager for SD Card"?  If so, that means the SD card is at least recognized by the system.  If that is the case, have you tried loading another disk image?

Antonio Tamairón

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Jan 23, 2026, 12:55:08 PM (5 days ago) Jan 23
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Hi,

Yes you are reason. I have noticed that SD card module is not recognized. I´m using this one below. (see image)
In principle all cables are correctly connected to the SPI head and SD was formatted to FAT type (any consideration about file format)
Is needed to configure something about SD card in config.h/config.cpp on source files? The menu that you are referring to is not shown in configuration menu.
SD Card Module – Wildware



Chris Davis

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Jan 23, 2026, 1:21:16 PM (4 days ago) Jan 23
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The one included in the kit is this one:
61Ntu--miHS._AC_SL1200_.jpg

I have never tried the one you have.

Antonio Tamairón

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Jan 23, 2026, 1:32:26 PM (4 days ago) Jan 23
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Yes its similar. 

I connected according to this pinout (head of the left side, SPI) Is it correct?

DUE          SD
MISO ---> MISO
MOSI ---> MOSI
SCK ---> SCK
VCC ---> VCC (5v)
GND --> GND

I have tested that DUE on SPI head has 4.5VDC then I connected to 5V pin on SD module HW-203


Arduino Due SPI - Due - Arduino Forum

Antonio Tamairón

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Jan 23, 2026, 3:01:06 PM (4 days ago) Jan 23
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I tested another SD module, in this case at 3.3v microSD module and the results is the same, not working. 

What could be happend? Thanks in advance 

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