Saturday, January 27, 2018

Processed more PARC cartridges, validated latest ethernet tool, and worked on Altair replica to HP terminal link


Before I can hook my USB to CDC mode TTL serial to the TTL to RS232 level serial converter and ultimately to the 2621A terminal, I have to talk to the USB device and update its communications settings. That conversation only happens over the wire TTL serial side, with the USB cable disconnected.

I have a DB9 serial connector on one of my computers, which I will use to configure the USB to serial module. I found an old DB9 based serial cable, cut it apart and wired it up to the module, crossing TX and RX. I hooked CTS and RTS together to keep the PC side happy. 

With 5V power applied to the module, I fired up a simple terminal program on the PC and did the configuration. I had to set the BAUD rate to 9600 and the transfer to byte by byte mode, without local echo.  However, when I hooked it up to the PC serial port and tried to communicate, I got nothing. That was true whether RX/TX were swapped or straight. 

I haven't used the PC port before, so there is a possibility that the hardware doesn't work right. I needed to figure out where the problem lies. It is possible it is that I don't have the magic combination set right, among all the darned DCD, DSR, CTS, and RTS signals, thus the port is blocked. 

The quick test was to hook the RX and TX lines from the PC cable together. Immediately, I saw my typed characters echoing back on the terminal program. This proves that the serial port is working, thus I have to focus in on the USB to serial module as the fault or something in my setup. 

Once I have a working link to the Altair replica, either this USB module or a Bluetooth to serial module,  I can wire it to the TTL/12V level shifter board. I looped CTS and RTS to the 12V side of the level shifter, which will in turn be wired to the Centronics 50 connector that will plug into the HP terminal. 

We were in Fry's today to pick up more 99.9% pure Isopropyl Alcohol before cleaning disk cartridges. I took the opportunity to grab a Bluetooth to Serial module as a backup means of linking my Altair to the HP terminal. 


Friday morning I aligned the drives with the recently cleaned heads, brought all forty cartridges down to the lab area and began archiving. We had run out of isopropyl alcohol to clean the surface of each disk and the heads, requiring a run to buy more supplies before continuing after lunch.

By the end of the day, we had processed fifteen cartridges, extracting each image and testing it under Contralto. We only had to wipe some fine oxide residue from the heads two times. The result was 13 good disk images.

The reason it wasn't fifteen was twofold. First, we found that one of the 15 cartridges had been previously archived by us, but our little stick on label (A) had fallen off at PARC. Second, we found another of the cartridges had two dings on the surface of the platter - small impact holes that exposed the aluminum underneath the oxide coating.

Those holes would likely cause a head crash, thus the disk was appropriate marked and skipped. These 13 recovered images were delivered to the software preservation archivists at Computer History Museum.


Ken put his latest rev of the board through a test program, proving out its full and correct operation. This board included all the pullup resistor and ringing suppression components he had added externally to prior boards.

One snag hit, however. The microSD card with the code for the device had fallen out back at his home, requiring Ken to rebuild the development environment on his laptop and then recompile the code for transfer to a new card. That took the remainder of the morning, before he could conduct the tests above.


  1. Re:serial port problems - "Black Box Catalog" used to have a patch plug consisting of two RS232 connectors with all lines brought outbto patch blocks but nothing connected. It was simple to jumper the connections you wanted.

    1. I keep hoping I have touched my last serial connection. A fixture like you described would be handy.