Chapter 6: The Keyboard

6.1 Description of the Keyboard

The keyboard of the 803 carries the word generator, the indicator lamps, the loudspeaker, the ‘clear store’ and other control buttons, and the ‘operate’ bar.

6.1.1 Word Generator

On the word generator section of the keyboard there are four rows of buttons. These contain 6, 14 6 and 13 buttons respectively, and correspond to the F1, N1 and B (together), F2 and N2 digits of a computer word. A depressed button represents a 1, and a released button a 0. When any button is pressed it locks down: the buttons in any row may be released by pressing the ‘clear’ button at the end of the row.

A decimal word generator has been fitted to some early machines. This has thirteen columns of 10 buttons each, labelled 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9. The buttons in any column are mutually exclusive: that is to say, depressing any button in a column releases the one already depressed. This set of 130 buttons is read in function 70 in various modes, depending on the setting of four mutually exclusive buttons provided for the purpose. However, for the operating steps described in 6.2 below, the ‘mode 1’ button should be depressed, so that the word generator is in "instruction" mode; that is to say, numbering the columns from left to right:

6.1.2 Indicator Lamps

The ‘display’ lamp is illuminated while the computer is switched on.

The ‘overflow’ lamp is illuminated while the overflow indicator is set.

The ‘parity’ lamp is illuminated and the computer stops when store parity fails. The lamp is extinguished as soon as the computer is restarted.

6.1.3 Loudspeaker

When the computer is in a dynamic stop, the maximum pitch is reached and maintained. The same pitch is heard for a short period when the computer is waiting fgor a busy line to be cleared.

6.1.4 Clear Store Button

While the ‘clear store’ button is in use, the computer does not stop if wrong parity is found in any location of the store.

6.1.5 Control Buttons and Operate Bar

The ‘read’, ‘normal’ and ‘obey’ buttons, the ‘selected stop’ button and the ‘operate’ bar are the principal means by which the operator controls the computer. Their use is described in 6.2 below.

The ‘read’, ‘normal’ and ‘obey’ buttons are together termed the ‘step-by-step’ buttons: they are mutually exclusive. The ‘selected stop’ button is a press-press button. The ‘operate’ bar is spring-loaded.

6.2 Manual Control of the Computer

To understand the use of the control buttons and the ‘operate’ bar it is necessary to have a little knowledge of the way in chich the computer works.

In the cycle of actions in which the computer carries out one function there are three phases, which may be summarised thus:

1. Determine which instruction to obey next.
2. Take a copy of this instruction from the store, and place it in the control unit.
3. Obey it.

Whenever the computer is stopped, whether by means of the control buttons or as a result of store parity failure, it is always in the position of having just completed phase (b). There is therefore an instruction in the control unit, waiting to be obeyed: this is termed the present instuction.

1. To stop the computer immediately

   Depress either the ‘read’ or the ‘obey’ button.

2. To cause the computer, having stopped, to obey the present instruction, and stop again:

   Depress, or leave depressed, the ‘obey’ button, and depress the ‘operate’ bar once.

3. To cause the computer, having stopped, to read one instruction from the word generator, and replace the present instruction thereby.

   Depress, or leave depressed, the ‘read’ button, set the instruction in the F1 and N1 buttons of the word generator, and depress the ‘operate’ bar once.

   (This instuction is obeyed when either (ii) or (iv) is performed).

4. To cause the computer, having stopped, to obey the present instruction, and continue then to obey the instuctions in its store at full speed:

   Depress, or leave depressed, the ‘normal’ button, and press the ‘operate’ button once.

5. To clear the store:

   Depress, in this sequence, the ‘clear store’ and ‘normal’ buttons, and the ‘operate’ bar. Wait at least 10 seconds. The press the ‘read’ or ‘obey’ button and release the ‘clear store’ button by pressing it again.

6. To cause the computer, while running, to stop before obeying either instuction in a specified location:

   Set the address of the specified location on the N2 buttons of the word generator and depress the ‘selected stop’ button. (On earlier machines is is necessary also to depress the ‘obey’ button.)

7. To cause the computer, having stopped, to start and run at full speed (as in (iv)), but to stop again before obeying either instruction in a specified location:

   As in (vi), then depress the ‘operate’ bar.

If the computer has stopped on a selected stop, and is then restarted with the same selected stop setting still on the buttons, it will, in general, obey one instruction only, and stop again. For if the first stop was before obeying the first instruction of a pair, and if this is not a transfer instruction, the next stop is made before obeying the second instruction of the same pair.

The following practice is recommended:

If the computer is stopped while it is obeying a programme, and one or more instructions are inserted from the word generator, as in (iii) above, the return to the programme should be by the method of Example 21, below.

Example 21

1. Depress the ‘read’ button.
2. Set 40 X on the F1 and N1 buttons of the word generator.
3. Depress the ‘operate’ bar.
4. Depress the ‘normal’ button.
5. depress the ‘operate’ bar.

6.3 Recent Additions to the Keyboard (April 1961)

In addition to the items described above, the latest models also have:

6.3.1 Manual Data Button

6.3.2 Step-by-Step Lamp

6.3.3 Busy Lamp

6.3.4 Other Buttons and Lamps