Remote-processing CAMBASIC Manual de usuario descargar pdf (Pagina 170)

Commands - 137

VARPTR

Numeric Fun ction

SYNTAX: VARPTR(variable)

PURPOSE: To return the address in RAM of the variable. This command is similar to VARPTR found in other

BASICs. Unlike VARP TR, the address of a string variable is returned directly.

REMARK S: variable is any CAMBASIC variable.

This function may be used to pass data other than single bytes to external machine or assembly

language r outines. It can find uncommitted RAM for tem porar y data stora ge. Use it to transfer da ta

from arrays to Flash or extended memory.

This function returns an integer value that is the address in memory at which the value of a specified

numeric variable or numeric array resides. VAR PTR w ill not return the address of a string array.

This function may be used directly in the PEEK or POKE functions and in the CALL statement for

memory address references.

The form at of the stored CA MBASIC variable values is as follows:

Numbers are first normalized to a standard fractional binary form, with the binary point to the right

of the sign bit of the mantissa, and stored in four bytes.

The least significant byte appears at the lowest addr ess. The first three bytes are the m antissa, with

the sign in the most significant bit of the third byte. A sign bit of “1” designates a negative value.

The fourth byte contains the exponent, in “excess 128” notation (i.e., the value is always positive

and equals the actual binary exponent plus 128). As an exam ple, the hexadecimal string:

LSB Man tissa MSB Exponent

MMMMMMMM MMMMMMMM S.MMMMMMM 1EEEEEEE

Mem Mem+ 1 Mem+ 2 Mem+ 3

The normalized binary notation yields decimal equivalents which may not be obvious. The floating

point numbers ar e shown w ith the LSB on the left. F or more infor mation see “A n Introduction to

Microcomputers, ” V olume 1, by Osborne/M cGraw– Hill.

Scalar (simple) and numeric array variables reside above a program in RAM and are relocated

upward as new program lines are entered.

Strings ar e stored one char acter per byte, with the left– hand char acter fir st. T he addr ess retur ned is

the left– hand character.

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Remote-processing CAMBASIC Manual de usuario Pagina 170