Elliott 803 Simulator - Loading Programs

In order to get a binary program tape into the 803, you must first load the tape into the tape reader. This was covered in the general handling page. Once the tape is in place, switch to the keyboard and set F1=40, N1=0. Note that F1 is always specified in octal, whereas N1 is decimal. If you haven't seen the 803 Keyboard before, you will notice that the four red buttons on the left are labelled F1, N1, F2, N2. The red buttons are used to cancel the settings in the row of black buttons to their right. The black buttons are also labelled with numbers, for F1 and F2 these are octal as this is always used to define instruction opcodes. The N1 and N2 are labelled with their decimal equivalents. In order to set numbers other than those on the labels you have to work out a combination of buttons so that the numbers add up to the desired value. Most of these are fairly easy to work out. If the number desired differs from that set, you probably need to cancel the current setting before starting to press buttons. This is done by pressing the red button on the left of that row.

To set F1=40, N1=0, simply press the leftmost black button on the top row (labelled 40) and press the red buttong on the second row to make sure all the N1 buttons are unset.

To load a program, the setting on F2, N2 are usually ignored, so don't worry about them unless the program description says they are important.

You next have to cause the computer to execute this instruction. This requires a sequence of button presses: first make sure that the 'Read' button is depressed. 'Read', 'Normal' and 'Obey' are interlocked so that only one can be depressed. The 'Read' operation transfers the keyboard settings to the instruction register and this takes place when you depress the 'Operate' bar which is the long bar at the front of the keyboard.

The next step is to enter 'Normal' mode. In this mode the computer alternates between executing the instruction in the instruction register, and fetching the next instruction from store. This is the normal state of the computer when running. To enter the 'Normal' state, press down the 'Normal' button, then press the 'Operate' bar. The computer will then enter the normal state and will execute instructions until halted by pressing 'Read' or 'Obey'. Obey can be used, with the Operate bar, to 'single-cycle' the computer, although this is rarely done except by the maintenance engineer!

The instruction '40 0' which was executed above, causes the computer to jump to location 0 in the memory, where resides the 'Initial Instructions'. These read in the binary program tapes and store them in the computer memory. There are two sorts of binary tapes, self-triggering and non-triggering. The first will automatically start to run the loaded program when loading has completed, whereas the second will need the operator to execute a jump instruction (40 xxx) in the same manner as used above, but with a specific address, specified in the program description.

The binary tapes provided with this simulator are of the self-triggering variety and should need no further action, though they may well require data tapes or some specific action to be taken. See the program description if this is the case.

A simple test program is provided which after loading will self-trigger and display a sequence of numbers on the Console Printer. This will repeat until the program is physically stopped, usually by pressing the 'Read' button.

Now that you know how to load a binary program tape, you might care to investigate the possibilities of writing your own programs in Algol 60 or Elliott Autocode. I don't (yet) have the binary tapes to run the Autocode, but the Algol Compiler is probably a much better point to start anyway. If you are interested, go on to the next page which describes the compiler and how to use it.

Alternatively, return to the simulator page.


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