Sharp PC-1500 Instruction Manual page 137

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C.1. Fixed Memory Area
Although all variables of the same IYPC arc utilized in the same man ner. they arc not treated
the same internally. The PC·1500 inclvdcs a " foxed memory" area with enough storage space
for 26 nvmeric variables and 26 character siring variabl01 (string size ol
16
characters). Co n·
seqvcmly the variables A through Z, and the variables AS throvgh ZS are permanently allocated
within 1his area.
All other variables. including those \vith
tv10
c: h aractcr n<Jmes.
are
allocated \•1ithin the main
mcmor' y area ot the computer. This main memory area is iilso shelred by the instructions of 1he
program, :ilthough the variables are allocated beginning at the opposite end of memory from the
Instructions. Because the program instructions and data share the same area it is possible for them
10
use up all available storage. In this case an ERROR in the range
177
through
18 1
will occur.
It is importar't to realize that the two memory areas are not treated the same upon profJranl
initiation. This is explained in the chart in the next section . Basically.
variable s
in the fixed
memory area ar· e never cleared except by an explicit CLEA R statement. Tho$· e in main memory
are cleared whenever
a program
is begun with the
RUN command.
One other idiO$yncrasy about the fixed memory area is that the data in this area may
be
redefined as a. n array whose name is@ (At Sign) , for numeric variables, and@$ for string variables.
Thus. the design
ation @(11 is
the same storage location as the variable A and
@
(26) is the same
storage location as the variable Z. The designation @S (5) refers to the same location as ES, and
the designation @S (20) refers to the same location as TS. For obvious reasons subscripts above 26
are not allowed. Notice that the arrays@ and @Sneed not be dimensioned before use.
C.2. COMPAR ISON CHAR T OF PROGRAM
INITIATION METHODS
RUN GOTO
OEF
Display is cleared.
y y
N
Cursor returns to fir"$t column.
y
N
N
WAIT interval is set to infinite. N
N N
Trace mode is altered. N
N
I
N
Fixed Memory Arca is cleared. N N
N
Main Memory Area is
cleared.
y
N N
FOR ·NEXT. GOSUB
y y
y
internal stack is cleared.
ON ERROR GOTO is
y
N N
cancelled.
DATA pointer for READ
y
N
N
operation is RESTOR Ed.
USING format is cancelled.
I
y
N
N
135
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