Apple II User Manual

1779 EB85 8D 29 A4 STA STIY+2

1780 EB88 8D 2C A4 STA CPIY+2
1781 EB8B A9 99 LDA #$99 ;STA INSTR

1782 EB8D 8D 27 A4 STA STIY
1783 EB90 A9 D9 LDA #$D9 ;CMP INSTR

1784 EB92 8D 2A A4 STA CPIY
1785 EB95 A9 60 LDA #$60 ;RTS

1786 EB97 8D 2D A4 STA LDIY+3
1787 EB9A 68 PLA

1788 EB9B 4C 27 A4 JMP STIY ;START EXECUTING STA (),Y
1789 EB9E

1790 EB9E ;PUSH X & Y WITHOUT CHANGING THE REGS
1791 EB9E 8D 2D A4 PHXY STA CPIY+3 ;SAVE ACC

1792 EBA1 98 TYA
1793 EBA2 48 PHA ;PUSH Y

1794 EBA3 8A TXA
1795 EBA4 48 PHA ;PUSH X

1796 EBA5 20 BA EB JSR SWSTAK ;SWAP X , Y WITH RTRN ADDR FROM S`
1797 EBA8 AD 2D A4 LDA CPIY+3

1798 EBAB 60 RTS
1799 EBAC

1800 EBAC ;PULL X & Y WITHOUT CHANGING ACC
1801 EBAC ;IT HAS TO BE CALLED BY JSR & NOT BY JMP INSTR

1802 EBAC ;SINCE IT SWAPS THE STACK
1803 EBAC 8D 2D A4 PLXY STA CPIY+3

1804 EBAF 20 BA EB JSR SWSTAK ;SWAP X , Y WITH RTRN ADDR FROM`
1805 EBB2 68 PLA

1806 EBB3 AA TAX ;PULL X
1807 EBB4 68 PLA

1808 EBB5 A8 TAY ;PULL Y
1809 EBB6 AD 2D A4 LDA CPIY+3

1810 EBB9 60 RTS
1811 EBBA

1812 EBBA ;SWAP STACK
1813 EBBA BA SWSTAK TSX

1814 EBBB A9 02 LDA #2
1815 EBBD 48 SWST1 PHA

1816 EBBE BD 06 01 LDA $0106,X ;GET PCH OR PCL
1817 EBC1 BC 04 01 LDY $0104,X ;GET Y OR X REGS

1818 EBC4 9D 04 01 STA $0104,X
1819 EBC7 98 TYA

1820 EBC8 9D 06 01 STA $0106,X
1821 EBCB CA DEX

1822 EBCC 68 PLA
1823 EBCD 38 SEC

1824 EBCE E9 01 SBC #1
1825 EBD0 D0 EB BNE SWST1

1826 EBD2 BD 08 01 LDA $0108,X ;RESTORE Y & X FROM STACK
1827 EBD5 A8 TAY

1828 EBD6 BD 07 01 LDA $0107,X
1829 EBD9 AA TAX

1830 EBDA 60 RTS
1831 EBDB

1832 EBDB ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
1833 EBDB ;GET A CHAR FROM TTY SUBR INTO ACC ,SAVES X

1834 EBDB 8A GETTTY TXA ;SAVE X
1835 EBDC 48 PHA

1836 EBDD A2 07 LDX #$07 ;SET UP FOR 8 BIT CNT
1837 EBDF 8E 2A A4 STX CPIY ;CLR MSB

1838 EBE2 2C 00 A8 GET1 BIT DRB ;A^M , PB6->V
1839 EBE5 70 FB BVS GET1 ;WAIT FOR START BIT

1840 EBE7 20 0F EC JSR DELAY ;DELAY 1 BIT