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74 lines
3.1 KiB
Plaintext
74 lines
3.1 KiB
Plaintext
Pointer Functions
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This library contains functions for basic pointer access and manipulation.
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These functions are intended to allow sequential reading and writing of
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individual bytes to arbitrary locations in memory.
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A pointer consists of any two consecutive bytes in Zero Page and is
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referenced using the single byte zeto page address (0-254).
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Note: There is no concept of a null pointer in C02. A pointer containing
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the value 0 simply points to the first byte of memory.
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Usage: at the beginning of the program use the directives
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#include <pointer.h02>
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The following application functions are defined:
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ptr, msb, lsb = Pointer Set: Set the contents of the pointer at
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ptrset(zp, &addr); location zp to the address &addr.
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Returns the zsro-page pointer location, address
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high byte, and address low byte.
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ptr, msb, lsb = Pointer Address: Retrieves the contents of the
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ptradr(zp); pointer at location zp.
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Returns the zsro-page pointer location, address
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high byte, and address low byte.
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ptr, b = Pointer Put: Stores byte of b at the address
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ptrput(zp, b); pointed to by the pointer at location zp, then
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increments the pointer contents.
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Returns the zsro-page pointer location and value
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written to address.
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b = ptrget(zp); Pointer Get: Retrieves the contents of the byte
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at the address pointed to by the pointer at
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location zp, then increments the pointer contents.
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ptrinc(zp); Pointer Increment: Increases the contents of the
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pointer at location zp by one.
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ptrdec(zp); Pointer Decrement: Decreases the contents of the
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pointer at location zp by one.
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ptr, msb, lsb = Pointer Add: Adds the 16-bit value specified by &addr
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ptradd(zp, &addr); or msb, lsb to the contents of the pointer at
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ptradd(zp,msb,lsb); location zp.
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ptr, msb, lsb = Pointer Add: Subtracts the 16-bit value specified by
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ptrsub(zp, &addr); &addr or msb, lsb to the contents of the pointer at
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ptrsub(zp,msb,lsb); location zp.
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r = Pointer Compare: Compares the contents of the pointer
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ptrcmp(zp, &addr); at location zp to the address &addr.
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Returns 255 if the contents are less than the address
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(pointing to a byte lower in memory), 0 if the contents
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are equal to the address (pointing to the same byte),
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and 1 if the contents are greater than the address
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(pointing to a byte higher in memory).
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These results can be evaluated using the C02 unary
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comparator ! or the test-operators :+ or :-.
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Note: This library expects the following to be defined:
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the transient variables
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temp0, temp1, temp2 Temporary storage
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