Commodore 1581 - Page 49

communications for this file can take place. The possible range of disk
channel numbers is 0-15, but 0 is reserved for program loads, 1 for
program saves, and 15 for the disk command channel. Also be sure
that no two disk files have the same channel number unless they will
never be open at the same time. (One way to do this is to make the
channel number for each file the same as its file number.)
"drive #" is the drive number, always 0 on the 1581. Do not omit
it, or you will only be able to use two channels at the same time
instead of the normal maximum of three. If any pre-existing file of the
same name is to be replaced, precede the drive number with the "at"
sign (@) to request OPEN-WITH-REPLACE.
"file name'1 is the file name, maximum length 16 characters.
Pattern matching characters are allowed in the name when accessing
existing files, but not when creating new ones.
"file type" is the file type desired: S = sequential, P = program,
U = user, A=append and L = length of a relative file.
"direction" is the type of access desired. There are three possi
bilities: R=read, W=write, and M = modify. When creating a file, use
"W" to write the data to diskette. When vie\^ing a completed file, use
"R" to read the data from diskette. Only use the "M" (modify) option
as a last ditch way of reading back data from an improperly closed
(Splat) file. If you try this, check every byte as it is read to be sure the
data is still valid, as such files always include some erroneous data, and
have no proper end.
"file type" and "direction" don't have to be abbreviated. They can
be spelled out in full for clarity in printed listings.
"file #", "device #" and "channel #" must be valid numeric
constants, variables or expressions. The rest of the command must be
a valid string literal, variable or expression.
"w" is an option that must be specified to write the sequential file,
or the file will be opened to read.
The maximum number of files that may be open simultaneously
is 10, including all files to all devices. The maximum number of
sequential disk files that can be open at once is three (or two if you
neglect to include the drive number in your OPEN statement), plus the
command channel.
EXAMPLES OF OPENING SEQUENTIAL FILES:
To create a sequential file of phone numbers, you could use:
BASIC 7.0: DOPEN#2,"PHONES",D0,U8,W
BASIC 2.0: OPEN 2,8,2,"0:PHONES,SEQUENTIAL,WRITE"
or
OPEN 2,8,2,"0:PHONES,S,W"
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