Recent Posts

Ben Sinclair's avatar

MFJ 9420

I boxed up my Icom IC-7100 to sell, as I want to swap it for the new Yaesu, so I've been using my MFJ 9420. The 9420 is a cheap 10W SSB rig that works surprisingly well!

It has a smooth analog tuning knob, a smaller fine tuning knob, and that's about it for controls. The top firing speaker actually sounds good too.

Paired with my MFJ loop I was able to make some SSB contacts today, and even got into a pileup or two.

Ben Sinclair's avatar

A New Project

I've just started building my own 6502-based computer, similar to computers built by hobbyists in the 1970s.

I selected the 6502 CPU because it seems simple to understand, there is plenty of documentation, and a large community exists around it. The chip pictured is actually a 6504, which is a 6502 in a smaller package. It won't be able to address as much memory because it lacks the pins to do so, but it will be easier to wire up.

Hopefully it will work!

Ben Sinclair's avatar

My IBM System 360

I recently purchased the name plate from an IBM System 360, which is one of my favorite machines. There are only around 30 known systems remaining, so I was happy to at least find a name plate.

One interesting note about this purchase... I ran across a mention in Resurrection (a computer history magazine) about a huge warehouse of System 360 machines in Texas. The IBM Hursley Museum was in touch with the owner, but he stopped talking to them.

My name plate was shipped from Texas, and the seller said he was parting out full systems from a warehouse, so it had to be the same person. I gave the museum any contact information I had, and hopefully they will get in touch again. These are very rare machines that need to be saved.

Here's a photo of a colorful IBM System 360 installation. Note the name plate above the console in the upper left.

IBM System 360

Ben Sinclair's avatar

The PDP-11 AUX Switch

One thing that tripped me up with my PDP-11/23 was the aux switch on the front panel. I assumed it simply controlled the auxillary AC power plug on the back, which is what some of the documentation says. You might use it to power an RL02 drive, for example.

I didn't realize that it can optionally control the line clock interrupt. My system suddenly started acting very strange, and was no longer able to boot XXDP via the TU58. It turned out I had flipped the aux switch, which was setup to control the line clock interrupt. After some help from the cctalk mailing list and the documentation, I found that the BVD11 can control the line clock interrupt via software if you set a certain jumper. Now I just leave the aux switch alone!

Ben Sinclair's avatar

Booting the PDP-11/23 from a TU58 simulator

Now that the PDP-11/23 will boot to ODT and run some test programs, it's time to try something more advanced.

Since I don't have any actual peripherals, I can use a TU58 tape drive emulator running via serial. I have four serial ports on the PDP-11, with one being used for the console. I can use another to connect to the TU58 emulator on a Linux machine.

I learned a few things in getting this running. First make sure the jumper settings on the DLV-11 are correct, and make sure to match the settings on your console and the serial port for the emulator on your Linux machine. Second, the TU58 emulator doesn't properly set the serial port settings on its own. To make it work I have to start the emulator, then use stty to change the settings before I attempt to boot. In my case, I run:

sudo stty -F /dev/ttyS4 38400 cs8 clocal -crtscts ixoff

Knowing how to wire wrap connections is another valuable skill when working with these machines.

With everything seemingly setup right, I tried to boot. Every time it would halt back to ODT after the same amount of reads. I guessed that my M8044 memory wasn't working right. It has a set of dip switches to configure the memory addresses, and I found that some of those switches had failed and wouldn't close (apparently a common problem). I soldered jumpers over the failed switches, but still had no luck.

I eventually found a replacement M8044 board and it worked!

xxdp boot

XXDP is minimal operating system and a suite of diagnostics for almost every piece of PDP-11 hardware. I'm able to run some of the diagnostics, but I can't seem to get my machine to pass the JKDBD0 CPU diagnostic. According to the diagnostic manual, it should at least print a banner when it starts, but I'm not even seeing that.

Unfortunately the details of this CPU test are only available on microfiche, and the Bitsavers archive doesn't have this one. At the moment I can't get past this point, but I'll keep trying!

JKDBD0 Failure