Commodore PET User Manual page 264

The second step is to OPEN the data file:
80
PRINT".~
OPENING MAIL FILE
~~":
OPEN 1,
L
2, "MAIL"
MAIL is opened as logical file #1 on the cassette unit. with an EOT mark to
be written at the CLOSE of the file. The message" OPENING MAIL FILE "is
displayed on the screen immediately prior to the actual OPEN command so the
user knows that the file is being opened Ut takes a few seconds to open the file).
Now the tape is ready to accept data. As data is input to the tape it should
also be input to the screen so the data may be checked for mistakes. Lines 130
through 170 input the data to the screen.
Variable "1" in line 90 is the incrementing record counter. displayed at line
100. Lines 130 to 170 accept each variable. NM$ (name) and Al $. A2$. and A3$
(addresses) as separate fields by keyboard input; the end of each field is signaled
bya carriage return. After ail four fields have been entered. line 180 instructs the
user to either change a field or save the record. If a field is incorrect. the user types
the field number (1-4) and the program jumps to a correction routine at line 280 to
change that field.
Depending on the field number input (variable X) the cursor is placed at the
specified field. allowing the user to change the field. and the program returns to
line 180 for the user to specify another field change. When ail the fields are cor-
rect and 0 is input. the program continues at lines 220 through 270 to write the
record on the data file. Each data item is written as a separate field by writing only
one data item with a carriage return per PRINT:#: commando The data is written to
the data tape as:
65 <CR> WIDGETSUPPLYCO <CR> 555 BOGUS AVE. <CR> GERTIE
Be sure the file number referenced by the PRINT# is the sa me one specified in the
OPEN statement.
After the record is saved. the program returns to line 90 to prepare for input
of another record. If you have no more records to enter. enter "END" for NM$.
Line 140 closes the data file and writes an EOT mark (specified in the OPEN com-
mand) when NM$="END".
You may have noticed that the tape does not move after each record is
saved. The PET stores ail the data to be printed in an "input buffer" until it is
written to the tape. When the input buffer is full. it writes a "block" of data
to the tape. A block may contain a partial record. a single record. or several
records. The PET leaves interblock gaps between each block of data. However.
vou need not be concerned with blocks except to understand that the PET reads
and writes data in blocks.
black
gap
black
gap
Figure 5-6 shows a flowchart of theMAIL.PRINT# program.
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