User`s manual

DOS Support Program

On your demonstration

disk, there may be a program called DOS

SUPPORT.This program, also called a wedge,allowsyou to use many disk

commands more easily (different wedges are used for the VIC 20 and the

Commodore 64). Just LOAD the program and RUN it. It automatically sets

itself up and erases itself when it's finished. You'll have a few hundred less bytes

to work with when this program is running, but you'll also have a handy way to

send the disk commands.

As a result of the DOS Support, the "/" key now takes the place of the

LOAD command. Just hit the slash followed by the program name, and the

program is LOADed. When you use this method, you don't need to use the

LOAD command or the comma 8.

Thc"(Q)"and ">" keys are used to send commands to the disk drive. If you

type (a$ (or >$), the directory of the disk is displayed on the screen, without

LOADinginto your memory! Thesekeysalsotake theplaceof the PRINT#(see

chapter 4) to send commands listed in the next chapter.

To read the error channel of the disk (when the red error light is blinking),

just hit either the (a'or the> and hit RETURN. The complete error messageis

displayed to you: messagenumber, text, and track and block numbers.

4: DISK COMMANDS

OPEN and PRlNT#

Up 'til now, you have explored the simple ways of dealing with the disk

drive. In order to communicate with the disk drive more fully, you have to

touch on the OPEN and PRINT# statements in BASIC(more details of these

commands are available in your VIC 20 or Commodore 64 User's Guide or

Programmer's Reference Guide). You may be familiar with their use with data

files on cassette tape, where the OPEN statement creates the file and the

PRINT# statement fills the file with data. They can be used the same way with

the disk, as you will see in the next chapter. But they can also be used to set up

a command channel. The command channel lets you exchange information

between the computer and the disk drive.

FORMAT FOR THE OPEN STATEMENT:

OPENfile#, device#, (command) channel#, text $

The file# can be any number from I to 255. This number is used

throughout the program to identify which file is being accessed. But numbers

greater than 127 should be avoided, because they cause the PRINT# statement

to generate a linefeed after the return character. These numbers are really meant

to be used with non-standard printers.