Live Display of Input Port

[Tom Lake]

In a real Altair 8800, you can enter a two-byte program that will display the input from a given port in real time. I use it to calibrate my cassette recorder by doing this:

000     333     INP

001     007     007

Location 0 has the INP (octal 333) and location 1 has the port number, 007 (cassette port)

You just enter the program, set the program counter to 0, then single-step twice. The data LEDs will then show whatever data is coming in from the cassette recorder in real time. You can adjust the volume of the recorder to see how the data is affected. I have recoded a tape with 15 minutes of octal 125 on it (01010101 binary) so I can immediately see if the data is being read properly and the cassette recorder is set to the proper volume level.

Does the AltairDuino respond the same way? I never tried it on my previous AD systems since I didn't have a real cassette recorder interfaced to them. Now that I've built David Hansel's backplane and boards, including the ACR board, I will use a real cassette recorder with the system and the above program becomes relevant again.

[udo....@freenet.de]

Test it with the FDC, I've used this program to make sure that such things work in the z80pack machines:

                   ;

                   ; TEST PROGRAM FOR THE 88-DCDD FLOPPY DISK CONTROLLER

                   ; SINGLE STEP TO WATCH ROTATING DISK ON DATA BUS LEDS

                   ;

   0100                    ORG 100H

                    

   0100   3E00             MVI  A,0        ;ENABLE CONTROLLER, SELECT DISK 0

   0102   D308             OUT  8

                    

   0104   3E04             MVI  A,4        ;LOAD HEAD

   0106   D309             OUT  9

                    

   0108   DB09             IN   9          ;LOOK AT SECTOR POSITION

   010A   DB08             IN   8          ;LOOK AT STATUS

                    

   010C   76               HLT

[da...@hansels.net]

Yes, the AltairDuino should respond the same way. Let me know if it doesn't.

Note that the cassette I/O board itself has an LED that comes on when it is seeing
proper levels from the cassette recorder. The light should be solid on while a tape
is running. If it flickers or even goes out intermittently then you need to change the
volume level.

[da...@hansels.net]

If you want to see the FDC status like Udo suggested, make sure you enable the "Force real-time mode"
option in the disk drive settings and that a disk is mounted.

[Tom Lake]

Thanks. I always do keep real-time mode active since I want as close to the original experience as possible. I am rather bummed that

the external backplane and its boards don't have interrupt capability but I understand that very few of us want to run Timesharing BASIC 

so it's not worth all the work necessary just for us few.

I would request simulating the turnkey board, though. That way we could switch out the ROMs and have access to the full 64K RAM.