Commodore Plus 4 - Page 376

364 Using Peripheral Devices
100 INPUT#1,B$
110 IFA$OB$THElirPRINTCHR$( 13)"VERIFY ERROR"
120 CL0SEl:PRINTCHR$(13):G0SUB130:END
130 IP(PEEK(64784)A1TD4)=OTHENPRINT//HIT STOP ON
DATASSETTE": WAIT64784,4
140 RETURN
Line-by-Line Explanation
10 Make sure no buttons are pressed on Datassette.
20 Open a data file for writing.
30 Get some input to record.
40 Output the string to the Datassette.
50 Close the file.
60 Make sure no buttons are pressed on Datassette.
70 Tell the user to rewind the tape, and wait for the button to be down.
80 Make sure no buttons are pressed on Datassette.
90 Open the file for reading.
100 Get the string from the Datassette.
110 Compare it with the string typed in by the user, and report error.
120 Close the file and make sure no buttons are pressed.
130 If a button is down, print a message, and wait until none are down.
140 Return to main program.
Using a Datassette from Machine Language
In general terms, you can choose one of two levels of communication when you
use the Datassette. At the higher level are the save and load routines that perform
all the necessary functions to save or load a section of RAM from disk. The lower
level allows the maintenance of an open file on the Datassette in addition to other
open files, similar to using OPEN commands in BASIC. These levels are explored
and example programs are given in this section. The complete descriptions of the
operating system subroutines used can be found in Chapter 5.
Saving, Loading, and Verifying Files The key subroutines for saving and
loading sections of RAM are S AVESP ($FFD8) and LOADSP ($FFD5). These