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When Is A Computer?

One Two's first custom program for your micro


A musical word-processor would be a very hip thing to have but would require much more computing power than is presently found in the average bed-sit. If we stop to consider exactly what is written on the scruffy pieces of paper which musicians pass around, we conclude that after orders for the takeaway, chord symbols and lyrics feature fairly heavily and musical notation proper is pushed into last place. With this in mind, the idea of harnessing a BBC micro and an Epson FX80 dot-matrix printer was born to take the donkey work out of providing chord charts for the whole band.

The first problem encountered is the lack of the necessary hieroglyphs for chord notation on the standard qwerty keyboard. Fortunately the Beeb allows us to define our own characters via the VDU23 command. By drawing 8x8 grids and doing a football pools job, the resulting patterns can be given numerical codes (horizontally, top to bottom, MSB top left) and the character assigned to a keyboard code. The Beeb manual says start user defined characters at code 224 and for fear of lightning bolts from the blue, we shall conform.

To get these characters to appear when certain keys are pressed is the next hurdle and what better than to use the bright red, "user definables" that take up the first row. To whip them into action the command *FX225,224 is used, rapidly followed by a *FX226,234. These operating system calls set the base address of the function keys to the desired 224 and also allow key shifting to make each one dual function.

As an exercise in delving into the inner workings of the Beeb this is fine, but more practically we need to be able to print these characters out as hard copy. This means going through the grid business again to define the characters for the printer. The Epson printer allows you to download a character set and the first task is to copy the standard set into the download memory area so that we don't have to define the whole works. The commands for these features are prefaced with an escape character (ASCII 27) and are sent solely to the printer by the VDU1,n function. A further command selects the download character set (as opposed to the original character set) and then after a suitable header the definitions follow as 8x11 matrices read vertically, MSB top, from left to right. Epson warn that adjacent horizontal dots must not be defined but this does not seem to limit character clarity.

Nothing should appear to happen when this program is run but to check that all is well you can just press the function keys and the character additions should be revealed. Having done its work the program can be scrubbed (assuming you have saved it on tape) by typing NEW and then, for the time being, it's up to you.

With the additions to the character sets of both micro and printer a great deal can be done with PRINT "...." statements but the cursor editing keys won't handle the user defined characters and the system is a far cry from the initial concept. In future articles you can expect further developments and details of special software offers from ONE TWO TESTING.

SOFTWARE


Chord chart processor

This month we start One Two's very own software service with a programme to let BBC micro owners write out chord charts on a screen and printer. In coming issues we'll be expanding the software to help write arrangements, prepare songs, keep track of home recording takes and transpose chords. The main programme is overleaf. Below are some examples of just a small part of its capability, and a guide to setting up for different printers.

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One Two Testing - Copyright: IPC Magazines Ltd, Northern & Shell Ltd.

 

One Two Testing - Sep 1984

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Computing


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> Grant Enlarger

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