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BREAKING A PROGRAM
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Frequently it is necessary to break a program when it gets stuck in
an endless loop, or when you realise that it is not running correctly. It
is possible to use either
<CTRL>-C or the RESET key. If you use the
RESET key then not only will the program be stopped, but the printer
will be switched off and output will be directed to the screen only.
However, if
<CTRL>·C is used, then the printer will not be switched
off and the error message will be printed on both the printer and the
screen. If you now try to re-run the program, all printing will go to the
printer as well as the screen from the beginning of the program.
PRINTING MONITOR LISTINGS
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You can also use the printer to dump areas of memory or
disassemble machine code, instead of printing just to the screen. If you
are in the monitor (the prompt will be a ") you can switch the printer
on by typing the number of the slot of the printer followed by
<CTRL>·P. However, if you are using DOS, the output will only go to
the screen and not the printer. This can be overcome by turning the
printer on in BASIC using
PR# 1 for slot I, before entering the monitor
using
CALL ·151 or CALL ·155.
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USE OF THE PRINTER
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WITH LOGO
Using the printer with the LOGO language is very similar to using
it with BASIC. The interface card has to be enabled, and the PRINT
commands then cause data to be printed on the printer rather than on
the screen. There are some peculiarities which require the control
codes to be sent in a specific way: these are described by means of
examples below. It is also possible to copy the screen to the printer.
Different versions of LOGO use slightly different commands to
control the printer. Examples are therefore given for APPLE LOGO
and MIT LOGO.
LISTING LOGO PROGRAMS
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The method of listing a program is the same as for BASIC. To print
out all the procedures in workspace:
• the printer is enabled
• the
PRINTOUT ALL or POALL command is typed in MIT and
APPLE LOGO respectively
• the listing is printed on the printer rather than on the screen.
The commands to control the printer are:
MIT LOGO
OUTDEV 1
OUTOEVO
APPLE LOGO
.PRINTER 1
.PRINTERO
action
switch to printer • the 'I'
denotes slot I
switch printer off
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The way you handle the computer after you have given these
commands at the prompt is slightly different with the two versions of
LOGO.
With MIT LOGO, everything LOGO would normally send to the
screen is sent to the printer instead but everything you type on the
keyboard goes only to the screen. This means that you can see what
you are typing by looking at the screen, but you have to look at the
printer to see LOGO's replies.
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