mirror of
https://github.com/RevCurtisP/C02.git
synced 2024-11-22 01:31:33 +00:00
74 lines
3.1 KiB
Plaintext
74 lines
3.1 KiB
Plaintext
Pointer Functions
|
|
|
|
This library contains functions for basic pointer access and manipulation.
|
|
|
|
These functions are intended to allow sequential reading and writing of
|
|
individual bytes to arbitrary locations in memory.
|
|
|
|
A pointer consists of any two consecutive bytes in Zero Page and is
|
|
referenced using the single byte zeto page address (0-254).
|
|
|
|
Note: There is no concept of a null pointer in C02. A pointer containing
|
|
the value 0 simply points to the first byte of memory.
|
|
|
|
Usage: at the beginning of the program use the directives
|
|
|
|
#include <pointer.h02>
|
|
|
|
The following application functions are defined:
|
|
|
|
ptr, msb, lsb = Pointer Set: Set the contents of the pointer at
|
|
ptrset(zp, &addr); location zp to the address &addr.
|
|
|
|
Returns the zsro-page pointer location, address
|
|
high byte, and address low byte.
|
|
|
|
ptr, msb, lsb = Pointer Address: Retrieves the contents of the
|
|
ptradr(zp); pointer at location zp.
|
|
|
|
Returns the zsro-page pointer location, address
|
|
high byte, and address low byte.
|
|
|
|
ptr, b = Pointer Put: Stores byte of b at the address
|
|
ptrput(zp, b); pointed to by the pointer at location zp, then
|
|
increments the pointer contents.
|
|
|
|
Returns the zsro-page pointer location and value
|
|
written to address.
|
|
|
|
b = ptrget(zp); Pointer Get: Retrieves the contents of the byte
|
|
at the address pointed to by the pointer at
|
|
location zp, then increments the pointer contents.
|
|
|
|
ptrinc(zp); Pointer Increment: Increases the contents of the
|
|
pointer at location zp by one.
|
|
|
|
ptrdec(zp); Pointer Decrement: Decreases the contents of the
|
|
pointer at location zp by one.
|
|
|
|
ptr, msb, lsb = Pointer Add: Adds the 16-bit value specified by &addr
|
|
ptradd(zp, &addr); or msb, lsb to the contents of the pointer at
|
|
ptradd(zp,msb,lsb); location zp.
|
|
|
|
ptr, msb, lsb = Pointer Add: Subtracts the 16-bit value specified by
|
|
ptrsub(zp, &addr); &addr or msb, lsb to the contents of the pointer at
|
|
ptrsub(zp,msb,lsb); location zp.
|
|
|
|
r = Pointer Compare: Compares the contents of the pointer
|
|
ptrcmp(zp, &addr); at location zp to the address &addr.
|
|
|
|
Returns 255 if the contents are less than the address
|
|
(pointing to a byte lower in memory), 0 if the contents
|
|
are equal to the address (pointing to the same byte),
|
|
and 1 if the contents are greater than the address
|
|
(pointing to a byte higher in memory).
|
|
|
|
These results can be evaluated using the C02 unary
|
|
comparator ! or the test-operators :+ or :-.
|
|
|
|
Note: This library expects the following to be defined:
|
|
|
|
the transient variables
|
|
|
|
temp0, temp1, temp2 Temporary storage
|