Commodore Plus 4 - Page 174

Reserved
Variable
Names
may be viewed as having rows and columns, with the first number
identifying the row and the second number in the parentheses identi
fying the column (as if specifying a certain grid on a map).
EXAMPLES:
A(7,2),BZ%(2,3,4),Z$(3,2)
There are seven variable names which are reserved for use by the
Plus/4, and may not be used for another purpose. These are the vari
ables DS, DSS. ER. EL, ST.TI, and TIS. You also can't use KEYWORDS
such as TO and IF, or any names thai contain KEYWORDS, such as
SRUN. RNEW, or XLOAD as variable names.
ST is a status variable for input and output (except normal screen/
keyboard operations). The value of ST depends on the results of the
last input/output operation. A more detailed explanation of ST is in the
Plus/4 Programmer's Reference Guide, but in general, if ihe value of
ST is 0 the operation was sucessful.
Tl and TIS are variables that relate to the real-time clock built into the
Plus/4. The system clock is updated every 1/60th of a second. It starts
at 0 when the Plus/4 is turned on, and is reset only by changing the
value of TIS. The variable Tl gives you the current value of Ihe clock in
1/60ths of a seconds.
TIS is a string that reads the value of the real-time clock as a 24 hour
clock. The first two characters of TIS contain the hour, the 3rd and
4th characters are the minutes, and the 5th and 6th characters are
the seconds. This variable can be set to any value (so long as all
characters are numbers), and will be automatically updated as a
24 hour clock.
EXAMPLE:
TIS - "101530" sets the clock to 10 15 and 30 seconds (AM)
The value of the clock is lost when the Plus/4 is turned off. It starts at
zero when the Plus/4 is turned on, and is reset to zero when the value
of the clock exceeds 235959 (23 hours, 59 minutes and 59 seconds).
The variable DS reads the disk drive command channel, and returns
the current status of the drive. To get this information in words, PRINT
DSS. These status variables are used after a disk operation, like a
DLOAD or DSAVE, to find out why the red error light on the disk drive
is blinking.
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