Commodore 128D User Manual page 319

VOL
WAIT
311
NOTE: If a graphic area is allocated or deallocated for use after a
SAVE, VERIFY and DVERIFY will report an error. BASIC text in this
case has been moved from its original (saved) location to another
address range. Hence, VERIFY, which performs byte-to-byte
comparisons, will fail, even though the program may be valid. See
also DVERIFY
—Define output level of sound
VOL volume level
This statement sets the default volume for SOUND and PLAY state
ments. VOLUME level can be set from 0 to 15, where 15 is the maxi
mum volume, and 0 is off. VOL affects all voices.
EXAMPLES:
VOL 0 Sets volume to its lowest level.
VOL 15 Sets volume for SOUND and PLAY statements to its highest
output.
—Pause program execution until a data condition is satisfied
WAIT (Location), <mask-1 > [,mask-2]
The WAIT statement causes program execution to be suspended
until a given memory address contains a specified bit pattern or
value. In other words, WAIT can be used to halt the program until
some external event has occurred. The data items used with the
WAIT can be any values. For most programmers, this statement
should never be used. It causes the program to halt until a specific
memory location's bits change in a specific way. This is used for
certain I/O operations and almost nothing else. The WAIT statement
takes the value in the memory location and performs a logical AND
operation with the value in mask-1. If mask-2 is specified, the result
of the first operation is XORed with mask-2. In other words, mask-1
"filters out" any bits not to be tested. Where the bit is 0 in mask-1,
the corresponding bit in the result will always be 0. The mask-2 value
flips any bits, so that an off condition can be tested for as well as an
on condition. Any bits being tested for a 0 should have a 1 in the cor
responding position in mask-2. If corresponding bits of the < mask-1 >
and < mask-2> operands differ, the exclusive-OR operation gives a bit
result of 1. If the corresponding bits get the same result the bit is 0. It
is possible to enter an infinite pause with the WAIT statement, in
which case the RUN/STOP and RESTORE keys can be used to
recover. WAIT may require a BANK command if the memory you
wish to access is not in the currently selected BANK.
BASIC 7.0 ENCYCLOPEDIA—Basic Commands and Statements