Elliott 803 Simulator - Paper Tape Editing

When computers were rare and paper tape was the thing, You had to spend quite a bit of time learning to use the paper tape editing system. This was based around a teleprinter with attached reader and punch. In the case of the Elliott 803, the favoured machine was a Creed Teleprinter, which had a separate tape reader, although the punch was attached to the side of the printer.

The simulator attempts to give you a feel for this by providing a simulation of the printer, reader and punch.

When you first go to the Editor page, you will see the printer has a keyboard, and if you click with your mouse on the keys, the character may or may not appear on the printer paper. If it doesn't appear, this may be because the printer is in the wrong shift for the character typed.

Let me explain about shifts. The paper tape used here has 5 holes across the tape. Actually, there are six, but the sixth is the feed hole and is smaller than the data holes. It is used to drive the tape through the reader. As there are only 5 holes, there are only 25=32 possible combinations. That's not enough to allow for 26 letter, 10 digits, 16 punctuations characters and other sundry features like 'carriage return' and 'line feed'.

Someone had the bright idea of splitting the character set into two halves, which for some reason are referred to as 'letter shift' and 'figure shift'. Two of the 32 combinations are reserved as shift characters and cause the printer mechanism to switch between the two states. A cunning machanism in the Creed keyboard locks out those keys which belong to the 'other' shift, and so they were not able to be depressed until the appropriate shift key had been pressed. The two shift keys are the longish keys at the bottom of the keyboard, labelled 'figures' and 'letters'. Certain keys are exempt from the shift system: 'carriage return', 'line feed', 'space' and 'runout' can be pressed in either shift.

Play about with the teleprinter, pressing keys and seeing what happens until you get the hang of it. When you have done that, you are almost ready to start typing a program. Before you do, you will need to turn on the punch. This is the box attached to the right-hand side of the printer. The yellow thing sticking out the bottom (or front on the real one) is the punch on/off lever and should be clicked to pull it out to turn on, then click again to push it back in to turn it off. Turn it on and watch as you type characters and they are punched into the tape. On the original system, you always punched about 3-6" of blanks to allow the tape to be loaded into a reader, but this isn't strictly neccesary here.

When you try punching a tape, you will realise that it is almost impossible to do so without making some typing errors. This is where the fun begins. What you have to do is complete punching the program, errors included, then edit the tape afterwards. You do this (carefully!) by putting the newly punched tape into the tape reader (below the centre of the keyboard) and copying the tape, making corrections as you go. To get the hang of it, I suggest you punch something short onto a tape. Tear off the tape by clicking on the tape somewhere between the punch head (which is across the middle of the punch, and the bottom edge of the punch. The tape will disappear, having been transferred to your hand. You can then click on the latch of the reader, which is a small black rectangle near the bottom of the reader. The tape will reappear across the reader.

Using the red buttons to the left of the reader you can cause the tape to be read and, at the same time, the characters are printed and, if the punch is switched on, punched onto a further piece of tape. The 'AUTO' button causes characters to be read at 10 characters per second. The 'MANUAL' button cancels the AUTO button and so stops reading. The 'SINGLE-SHOT' button reads a single character and copies it. Use the AUTO button to make a second copy of your piece of tape. Throw away the first piece by first clicking on the pink button above the reader, then clicking on the waste-paper bin. Next time around, try running AUTO until you approach your first error, pressing MANUAL to stop before the error character(s) have been printed and punched. Use the single-shot button until the error character is the next to be read, switch off the punch and single-shot over characters to be deleted, type in omitted or replacement characters as needed. If there is a significant chunk of text that is correct, use Auto, for very short stretches use Single-Shot, until you have corrected all your errors, the use Auto to complete thye copying. If you are anything like me you will end up with this second copy slightly improved, but still containg a few errors. Repeat the process, making a third, even more correct copy until eventually you have a completely correct tape. When you get experienced at it, you will find that you can do all corrections in a single pass, but don't be disheartened if it takes several at first. Throw all the failures in the bin and retain only the final copy.

Note that the printed copy will contain characters that you have deleted as well as newly-inserted characters. If you want a really accurate printout for your records, you have to run the final tape through a further time, with the punch turned off, of course, we wouldn't want to waste paper tape, would we?

There are two white squares on the editor page, these are places where you can put a tape temporarily if you need to. These areas also appear on the reader and punch pages and can be used if you need to prepare, for example, two or three different data tapes. The tapes put down on one page are visible on the other pages.

At some point you will be able to label a tape by clicking on the pencil but I haven't implemented that yet.

One final point. If you get really fed up of clicking on the Creed Keyboard with your mouse, you may discover that you can type characters in via your computer keyboard. Even better, the problem of Shift characters disappears, as these are magically inserted for you.

The plan is to be able to provide a means whereby you can prepare a file using your favourite editor, and import these into the simulator, and also to export the punched tapes or printed output into files, but, again, this is not yet available. Sometime soon, hopefully!


Page created by Bill Purvis, last update 29th November, 2004