Our First Laser Printer

We decided to purchase a laser printer so we could print bill of materials sheets for each job. I managed to find a used HP LaserJet cheap. This was the original LaserJet printer model and had only 128K of RAM. This was fine, except if you wanted to print graphics. You could not even draw a half page of black and white graphics with 128K. This also meant that there was very little room to load fonts into the printer. The saving grace was that there was a font cartridge slot. I bought one of those super font cartridges that had lots of fonts. It turns out that we really only needed one font. I don't remember which one we used, but it was a small monospaced font.

The printer had a serial port, not a Centronics printer port. Normally this would have been considered a limitation, but this was perfect for our shop floor control system which I was building around Arnet multiport RS-232 cards.

I needed to learn just a little bit of Hewlett Packard's PCL (printer control language) to make the LaserJet do its thing. I wrote some code in Smalltalk to drive the printer. Depending on how complex the board design was, these bills of materials sometimes had a lot of information on them. It was somehow very satisfying to produce software that would drive a printer elsewhere in the building. I had never done that before.

The printer was located up in the engineering department, and after they designed a circuitboard for an order they would fill in some fields into the shop floor control system and print out the bill of materials on the LaserJet.

My Skunk Works Project

What is a skunk works? A definition from Wikipedia: The designation "skunk works", or "skunkworks", is widely used in business, engineering, and technical fields to describe a group within an organization given a high degree of autonomy and unhampered by bureaucracy, tasked with working on advanced or secret projects.

In order to prototype the multiuser shop floor control system, I needed a real video terminal. The idea would be to take a computer and install one or more multiport RS-232 cards and connect terminals to them from all over the building.

The following work was done more or less under the radar. I wasn't trying to get away with anything, but I hoped to surprise Bob with the results I hoped to achieve. I managed to requisition an old Lear Sieglar ADM-3A terminal on the cheap. This was one of those pastel blue terminals with a "space age bubble" look to it. Needham High School had a few of these connected up to their PDP-11.

In order to make this work with Smalltalk/V I needed a tiny machine code routine so I could make calls to the serial port. I was lucky to find someone on a bulletin board who was kind enough to write this for me. I was even luckier that it worked! The machine code file was only 14 bytes long!

It didn't take me very long at all to create a master monitor, a login routine, a simple command parser, a simple job object, departments that could hold jobs, and the ability to move the work from one department to another and list the contents of each department.

What was absolutely most amazing about what Smalltalk/V made possible is that the system was extensible and debuggable... as it ran! If there was a runtime error while executing some command from the terminal, a debugger opened on the computer screen. I could then fix the bug right there, and the terminal could be restarted without bringing the system down for a recompile.

This was very promising to say the least.