Radio Shack TRS-80 Model II Reference Manual page 217

Technical Information
While a file is Open, the filespec is replaced with information used by the
System for bookkeeping. When the file is Closed, the original filespec (except
for the password) will be put back into the
DCB.
Important Note: Do not ever modify any portion of the
DCB
while the file is
Open. If you do, the results will be unpredictable.
Parameter List (11 bytes)
CONTENTS OF PARAMETER LIST (SAMPLE)
0070 0071 08 58
~
80
~
2 00
BUFADR RECADR EODAD "R" or "W" RL "F" or "V" 0 or 1 USER
or
"p"
or 2 ATTRIBUTE
BUFADR (Buffer Address). This two-byte field must point to the beginning
of the Buffer Area.
The Buffer Area is the space
TRSDOS
will use to process all file accesses. If
spanned records are possible, you must reserve 512 bytes.
If
no spanning is
possible, reserve only 256 bytes.
With Fixed Length Record files, spanning is only required when the record
length is not an even divisor of 256. For example, if the record length is 64,
then each physical record contains four records exactly, and no spanning is
required. In this case, reserve only 256 bytes for processing.
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