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Full title Utilities Tape - printscan
Year of release 1985
Publisher Boldfield Computing
Producer / Author(s) Charles Wehner
Memory 3k
Type AceForth Word
Original Cost £9.89
Instructions Click to download

This routine is one of five words saved on the cassette and further words included in the main programs ZX-PRINTER and WORDACE, which are intended for the advanced user. These enable a wide range of printing options to be generated and customised for your own specific purposes.

However, before these are used, some explanation is required of the principles involved. Usually, the most condensed form of creating information (such as graphics characters) is by means of an algorithm which works like a mathematical formula.

However, complicated and virtually random characters (such as the alphabet) are not readily described in this way, and they have to be stored explicitly in a data array or 'look-up-table'. The words provided here encompass both techniques. When the second method is used, you will see an associated dot addressable array, normally called DOTFILE present (eg. THINPRINT, WORDACE etc.).

You will also see that some operations are performed by supporting words which can be used separately if required. For example, the ITALIC Font uses SLOPE, and the sideways printing in WORDACE uses TURNDOTS.

Whilst most of the words are useful in their own right, the real intention is to illustrate the methods adopted and hence to allow the experienced user to write his own programs based on the same routines.

PRINTSCAN (load printscan) contains several new commands.

The machine code primitive called PRINTSCAN prints a single scan of dots on the printer and needs a 32 byte buffer to hold the 256 potential dots that form a line.

PRINTSCAN also requires the address of the first byte on the stack. This command is particularly useful in the creation of graphs, which in turn could be generated by data logging from some external equipment. To see a typical graph plotted, enter:
ZIGZAG Because it is likely that data logging will be performed as a background activity, multitasking is included.

Enter:

MULTITASKING to initialise the example.

You will note that the normal 'OK' prompt of the ACE is replaced with the message 'MULTITASKING' to remind you of the new status. In this case the previous graph generated by ZIGZAG is now plotted at the rate of one scan per minute, and you can be doing other computing at the same time!



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