Unable to get the Disk Mon menu

[Geoff Healey]

Hi, I am hoping for some suggestions/help.

I have built the disk controller with the V1.1 board but after much checking I have no luck getting it to display the mon menu. I have included some pics of the link/switches and the status of the USB-UART and a screen capture of what I get occasionally on the PUTTY terminal but here is a summary of what I have experienced.

 If I connect the PC to the UART before turning on the ALTAIR both leds (I assume TXRX) are on. Turning on the ALTAIR will most likely cause the brighter led closest to the disk cable connector to go off but pressing a key on the PC will cause the dimmer one next that flash. On other occasions both leds on the UART go off when the ALTAIR is turned on. I hold the monitor, momentarily push the reset and continue to hold the monitor I never get the prompt or any other characters on the screen no matter how long I hold the monitor (minutes in some cases). I do sometimes get some output with the return key (no other keys output) and I have attached a screen capture of that. If when turning on the ALTAIR both leds on the UART extinguish I never get any output to the screen but the dimmer led still blinks with keystrokes.

I have checked the board visually and with a multimeter for shorts and to ensure all the IC pins are in their sockets and all the components are of the correct value. The baud rate is 115200 8 bits, Ive tried all the flow control options in PUTTY but no change.

I guess the only unknown is the ATMEGA and if it is correctly programmed. I have seen mention of the fuses but I am not sure if following David Hansels instruction for those without a micropro programmer does set the fuses. I have programmed it via a UNO and tried both the MITS and ICOM hex files. Any confirmation of this would be good. https://github.com/dhansel/Altair8800-IOBus/blob/main/04-disk-controller/README.md

If there are any suggestions on diagnosing this I would be very grateful. What I am also not clear on is there any particular mode the ALTAIR needs to be booted in (switches etc) for the mon to be accessible via the UART. 

[M M]

1st drawn to the circle, but then it look like that ground short isn't connected?

[Geoff Healey]

Hi, The pic isnt clear but there is definitely a link between GND on the UART and GND on the board. And yes that solder joint looks dodgy but after checking / resoldering just to be sure no change in the status. Than you for pointing these out.

[Geoff Healey]

It was quite a while since I programmed the Atmega and I dont recall any errors. However today I tried again with a new Atmega chip and I am getting compiling errors related to the XModem library. If I use the Xmodem library files from Davids GITHUB I get 1 lot of errors and if I use the Arduino standard library I get another lot. I am wondering if any one else has had similar problems and could suggest where I can go from here. I have attached the output from the IDE for both the standard and David's Xmodem Lib. I followed the instructions as listed in Davids GITHUB page https://github.com/dhansel/Altair8800-IOBus/blob/main/04-disk-controller/README.md

[da...@hansels.net]

It looks to me like the compiler is getting confused because you have an XModem library installed and the Firmare-MITS code also comes with an XModem implementation but both implementations are different and not compatible with each other. 

In your "Standard Xmodem" output the compiler is trying to use the Arduino XModem library which fails because it's got a different interface than what the Firmware-MITS code expects.

In your "DavidH_Library" output  the compiler is trying to include both XModem.h files which then produces "redeclaration" errors. 

Try completely uninstalling the Arduino XModem library (i.e. the files in /Users/geoffhealey/Documents/Arduino/libraries/Xmodem).

[Geoff Healey]

Hi David, thank you for your suggestion. I did just that and now the download completes with no errors but unfortunately even with a new Atmega chip all the original symptoms are back - unable to get the monitor prompt, output as per the screen capture at the start of this topic.. Other than building a new board from scratch I am a stuck I think. Perhaps there is a faulty chip interfering with the Atmega prompt routine but its impossible to say from here.

[Geoff Healey]

I have built a second floppy controller but alas I get the same results as I did with the 1st one. I compiled a MITS and ICOM Atmega and the Arduino did not report any errors. I had to share the 74LS07's between the boards as I couldnt get another 2 locally (awaiting on a shipment). I am hoping someone who has made the controller and programmed the ATMEGA using a Arduino UNO would be willing to share their email address with me so I could ask some questions. Just a note my backplane works fine with the led and cassette boards in all slots so I confident the issue must be on my controllers and common to both. Any assistance would be great. Warm regards Geoff

[da...@hansels.net]

I'm not sure what is going wrong but a few things to check:

- Triple-check that your serial terminal is set to 115200 baud. Maybe test with some other device (e.g. the AltairDuino)  that your serial terminal works properly with a device talking at 115200 baud.

- To rule out that a broken 74LVC245 may disrupt your serial communication, remove U5 from the board and then try again.  If it works without U5 then it's likely a problem with that or possibly U3

- If you have access to an oscilloscope, probe the TX signal coming out of the disk controller board. Does it look like a 115200 baud serial signal?

- One possible reason for failing serial comms could be that the ATMega chip is running at the wrong frequency. Are you sure you set the board type to "ATMega328P (5V, 16MHz)" BEFORE buring the bootloader? The 16MHz is very important.

- Maybe the crystal has a problem and not outputting 16MHz - easiest to check with an oscilloscope.

David