April/May 1980, Issue 7

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D-BUG has several commands. These are entered by typing a colon followed by the command letter. An excellent feature is the alternate video RAM command, :0. This specifies a 1K block of RAM which is spare in your system. It can be swapped with the NAS-SYS/D-BUG display by using the command :A, pressing Enter returns the display to normal. The two pages of the display are automatically swapped over during execution (E or S commands), so that use of the screen for debugging does not affect the display used by the program. This is invaluable for testing programs which output information to the display and read it back. (Don’t forget to clear the alternate display before running your program! Use :A then clear the screen).

D-BUG works by trapping all output via the UOUT jump, Since this means the the UOUT jump has been used up and is no longer available, for example, for driving a parallel printer, D-BUG provides a command (:C) to set the address of your own U output routine.

A further feature is the :F command, which is used to find a string of up to eight consecutive bytes. Even more, one or more of the bytes may be specified as ‘wild’, for instance, if D-BUG were asked to Find 2A – 0C (the ‘dash’ means ‘wild’), D-BUG would find every location where HL was loaded from a location between 0C000H and 0CFFH.

The only slight problem you might encounter fs if D-BUG is activated while running a program which outputs a colon as the first character of a line. D-BUG instantly grabs control and obeys’ the “command”!

D-BUG is acivated by typing the command E C009 and can be de-activated by the N command. A Nascom 2 can be set to power up at C000H, and in this case D-BUG is activated on power up or on pressing Reset. It is necessary to re-activate D-BUG after using ZEAP.

Remember, you must have NAS-DIS and NAS-SYS in your system before you can use D-BUG. We have tried D-BUG thoroughly, and have found it to work well, we recommend it as a ‘must’ for all machine code addicts.

D-BUG was written for Nascom by Mick Scutt of CC SOFT, and is available from Nascom through your local dealer. Contact your dealer for details, and again if he doesn’t know anything about it, have a go at Nascom Sales Department for prices and availability.


Some time ago Crystal Electronics announced an 8K Basic for Nascom 1. They have not stopped at that but have continued work on improving it, and recently announced a completely new version Basic 2.2, which is for Nascom 1 or 2 using T2, B-BUG, T4 or NAS-SYS monitors. Since it has several major improvements over the previous versions, we have decided to review it and compare it with the Nascom 8K Basic.

XTAL is a standard floating point 8K Basic, although in fact it is only about 7.25K long. Crystal jokingly describe it as a 16K Basic

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