Sharp PC-1500 - Page 137

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C.1. Fix ed M em ory Area
Although
all variables of the same IYPC arc utilized in the same manner. they arc not treated
the same internally. The PC·1500 inclvdcs a " fo x ed memory" area with enough storage space
for
26 nvmeric variables and 26 character siring vari abl01 (string size ol 16 cha racters). Con·
seqvcmly
the variables A through Z, and the variables AS throvgh ZS are permanently allocated
within 1h is a rea .
All other variables. including those \vi th tv10 c:haractcr n <Jmes. are allocated \•1ithin the ma in
mcmor'y area ot the computer. Th is main memory area is iilso shel red by the instructions of 1he
program, :ilthough the variables are allocated beginning at the opposite end of memory from the
Instructions. Becau se the p rogra m instructions and data share the same area it is possible for them
10 use up all avail ab le s to rage. In this case an ERROR in the range 177 through 181 will occur.
It is importar't to rea li ze that th e two memory areas are not tr eated th e same upon profJranl
initiation. This is ex pla ined in th e chart in the next sec ti on. Ba sically. variables in th e fixed
memory area ar ·e never c leared except by an explicit CLEAR statem ent. T ho$ ·e in main memory
are cleared wh eneve r a program is begun with the RUN comm and.
One other idiO$yncrasy about the fix ed memory area is that the data in th is area may be
redefined as a.n array whose name is@ (At Sign), for numeric variables, and@$ for string variables.
Thus. the designation @(11 is the same storage location as the variable A and @ (26) is th e same
storage location
as the variable Z. The design at ion @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.
CO MPARI SON CHART 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
M ain Memory Area is cleared.
y
N N
FOR·NEXT. GOSUB
y y
y
int erna l stack is clea r ed.
ON ERRO R GOTO is
y
N N
cancelled.
DATA po inter for R EA D
y
N
N
operation
is RESTORE d.
USING format is cancelled.
I
y
N
N
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