Jon Relay's Apple II Info Archives
Zero Page Addresses
$00-$05 - ???
$06-$09 - Free Space
$0A-$0C - JMP to USR() User Function Routine
$0D-$17 - ???
$18 - First Data Track
$19 - First Data Sector
$1A-$1B - Shape Pointer for DRAW
$1C - Last COLOR Used
$1D-$1E - Free Space
$1F - ???
$20 - Left Margin (0 - 39/79, 0 is default)
$21 - Width (1 - 40/80, 40 is default, 0 crashes Applesoft)
$22 - Top Margin (0 - 23, 0 is default, 20 in graphics mode)
$23 - Bottom Margin (0 - 23, 23 is default)
$24 - Horizontal Cursor Position (0 - 39/79)
$25 - Vertical Cursor Position (0 - 23)
$26-$27 - Address of Byte Containing X,Y
$28-$29 - Base Address of Text Cursor's Position
$2A - ???
$2B - Boot Slot * 16
$2C - Lo-Res HLIN/VLIN Endpoint
$2D-$2F - ???
$30 - COLOR Value * 17
$31 - ???
$32 - Text Mask ($FF = Normal, $7F = Inverse, $3F = Flashing)
$33 - Prompt Character
$34-$35 - ???
$36-$37 - Address of Output Routine
$38-$39 - Address of Input Routine
$3A-$4F - ???
$50-$51 - Result of the Conversion of the FAC to a 16-Bit Integer
$52-$66 - ???
$67-$68 - Address of Beginning of BASIC Program ($0801 is default)
$69-$6A - Address of Beginning of BASIC Variables
$6B-$6C - Address of Beginning of BASIC Arrays
$6D-$6E - Address of End of BASIC Variables
$6F-$70 - Address of End of String Data
$71-$72 - Address to Move String To
$73-$74 - Address of Beginning of String Data
$75-$76 - Current Line Number Being Executed
$77-$78 - Line Number Where END or STOP or BREAK Occurred
$79-$7A - Address of Line Number Being Executed
$7B-$7C - Current Address of DATA
$7D-$7E - Next Address of DATA
$7F-$80 - Address of Input or Data
$81-$82 - Last Used Variable's Name
$83-$84 - Last Used Variable's Address
$85-$9A - ???
$9B-$9C - Pointer for $D61A and $F7D9
$9D-$A3 - Floating Point Accumulator (FAC)
$A4 - ???
$A5-$AB - Floating Point Argument Register (ARG)
$AC-$AE - ???
$AF-$B0 - Address of End of BASIC Program
$B1-$B6 - Subroutine to Increase the String Data Pointer
$B7-$BE - Subroutine to Return the Character Pointed to by the String Data Pointer
$BF-$CD - ???
$CE-$CF - Free Space
$D0-$D3 - ???
$D4 - Error Code Flag
$D5-$D6 - ???
$D7 - Free Space
$D8 - Error Flag (Bit 7 Set if an Error Handler is Used)
$D9 - ???
$DA-$DB - Line Number Where Error Occurred
$DC-$DD - ???
$DE - Error Code
$DF - ???
$E0-$E1 - Horizontal Coordinate of HPLOT
$E2 - Vertical Coordinate of HPLOT
$E3 - Free Space
$E4 - HCOLOR Value (0=0, 1=42, 2=85, 3=127, 4=128, 5=170, 6=213, 7=255)
$E5 - ???
$E6 - High Byte of Address of First Byte of Where HGR is Plotted
$E7 - SCALE Value (0 = 256)
$E8-$E9 - Address of Shape Table
$EA - DRAW/XDRAW Collision Count
$EB-$EF - Free Space
$F0 - ???
$F1 - SPEED Value (Subtracted From 256)
$F2 - ???
$F3 - Text OR Mask for Flashing Text
$F4-$F5 - Address of Error Handler (Line Number after ONERR GOTO)
$F6-$F8 - ???
$F9 - ROT Value
$FA-$FE - Free Space
$FF - Used by Applesoft's STR$ Function
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