Apple IIe - Appendix I. Machine Language Subroutines

Appendix I 301
Appendix I. Machine Language Subroutines
The Apple lle's operating system has been written as a series of
subroutines. These subroutines can easily be used in the user's
own programs . In order to use these subroutines , load the 6502's
registers with any necessary data . Then execute a jump to
subroutine (JSR) to the subroutine's starting address.
Although the starting addresses and functions of the monitor
subroutines are identical in the Apple II+ and Apple lie, the
routines themselves are not. For this reason , if a program is to be
compatible with both machines , it must only call monitor
subroutines at their starting address.
The descriptions of the subroutines will be as follows.
NAME (address)
description
A = 00 X = 00 Y = 00
The values of the 6502's accumulator (A) , X-register (X) , and
Y-register (Y) after the execution of the routine are given on the
same line as the name and starting address. A "??" indicates that
the register's contents have been scrambled . A"--" indicates that
the subroutine has not changed the contents of that register.
Hex values shall be indicated with a prefix of"$".
BELL ($FF3A/65338) A= $87 X = -- Y = --
BELL writes the CONTROL-G (bell) character to the current
output device .
BELL 1 ($FBDD/64477) A = ?? X = ?? Y = --
BELL 1generatesa1000 Hz tone with a duration of 0.1 seconds on
the console speaker .