Commodore PET - Reading a Data File

READING A DATA FILE
After vou have written information to a data file. in order to use it in
another program vou must be able to read the information off the tape and
put
it into memory.When the PET reads a data tape it transfers the data to an "in-
put buffer" before sending the data on to memory:
Memory
PET
Input
Buffer
The input buffer hoIds up to 191 bytes of data. The data is read off the tape
until the input buffer
is full. When full. the PET temporarily stops the tape.
and transfers the data to its proper location
in memory.
You can see this happen if you read large quantities of data at a time: the
tape stops
for several seconds while the input buffer "dumps" the data into
memory. Once emptied, the tape will move again as more data is read. A
flowchart of this process is shown in Figure 5-7.
Reading a data file
is similar to writing one. The four main steps are the
same (except
that the file is read instead of written):
1. LOAD the program file
2. OPEN the data file
3. Read the data file
4. CLOSE the data file
Step 1:
Like writing to the tape, you must code your program to read the
data file.
Code and type the program into PET memory and save it on tape.
Later, the program may be loaded when needed. Remember that the commands
to open, read, and close the data file are programmed within the program file.
Once the program file
is loaded, mount the data tape. Then execute the pro-
gram using the
RUN commando
Step 2: When the data file is opened it must be referenced with the
same physical device number and file name
it was assigned in the write pro-
gram.
A different logical file may be assigned, and the secondary address code
must
be 0 for the READ option.
Write Program Read Program
OPEN 1.1.2."DATA" OPEN 1.1.0,"DATA"
Ll--
t
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