Nascom News­let­ter

The relevant location will depend on the version of NAS-DOS which you are using:

Those of you with EPROM blowers can change the relevant location to suit your drives if necessary. Do remember the usual precautions and keep the original chip in case of accidents during the modification process.

6. Disc Files

As well as allowing programs to be stored on disc NAS-DOS allows data to be staredand loaded. Routines are provided within NAS-DOS itself to assist in data storage and retrieval, and these can be accessed directly from assembly language and Nascom ROM BASIC. ROM BASIC was developed long before discs were available on the Nascom system, and therefore the language itself does not provide any disc commands. Access to the disc is therefore achieved by patching in the various NAS-DOS routines. This is done by means of the USR( ) function in BASIC, the argument being the number of the NAS-DOS routine to be called. It is of course necessary to DOKE 4100,-10234 to point the USR routine to an appropriate translator in NAS-DOS itself. This slightly awkward technique is necessary to allow the commands to be added to a ROM BASIC – it is not a limitation of NAS-DOS. More recently implemented languages (eg Extended BASIC) and applications programs (eg NAS-CALC) include within them meaningful commands for direct access to the discs via NAS-DOS. The DIR (directory) command is an example of this facility.

Before any disc commands are used in a BASIC program under NAS-DOS the command

DOKE4100,-10234

must be executed by the program to set up a link to the NAS-DOS Commands. You must then initialise the NAS-DOS commands and data area with an instruction of the form

A=USR(1)

When using subsequent disc commands remember that the number of the disc drive is stored in location 3360 (decimal), so if you want to change the disc drive accessed you must include in the