Nascom News­let­ter

4. CORRECTIONS

One or two corrections need to be made to previous articles. Firstly the parallel printer driver from BASIC, section 3.2 of the April newsletter. In line 80 the final value is shown as 217, when it should be 201. This error originated in Application Note AN-0006, and was due to an error in converting hex to decimal (I should have used the computer!). The error is also present in the current BASIC manual. In the same article the listing seems to have got slightly corrupted at line number 5 – there should be a line

PORTA   EQU   4

to declare the A port address – this seems to have become merged with a preceding comment line.

Secondly the keyboard interrupt listing in the last issue. I merged this into the SPEX word processor file without looking properly at the line length. You may therefore find the layout has been right justified on some long lines, producing an odd appearance, depending on how the Editor formatted the pages when producing copies for the newsletter. This should still be understandable, but is a function of how the text was formatted rather than being a fault in NAS-SEMBLER.

5. USEFUL INFORMATION

Some users have asked about the access times of different versions of the Nascom disc drives and the values used in NAS-DOS. The earler Nascom drives had a 30 mS access time, while the latest half height units have 6 mS access time. The different versions can be recognised as follows, listed in chronological order:

1. Earliest drives, all plastic sides (no inset metal plate). Small horizontally mounted pot in the centre of the PCB mounted on the drive. These are 30 mS drives, but many can be made to run at 20 mS, although you may need to tweak the pot.
2. As above, but no pot fitted. These will usually only run 30 mS drives.
3. As 1.
4. Small metal plates mounted on each side of the drive which carry the mounting screw. These ae 20 mS drives.
5. Half height drives. These have a 6 mS access time.

The access time is controlled by outputting a byte at one point – NAS-DOS. This byte is interpreted as follows: