Editing Sad Mac Error Codes (section)

== Common Exception Codes (Class 0F) ==

When the major class is '''0F''' on a compact Mac, or when the exception byte is ORed into the major code on an expanded-format machine, the subcode tells you which [[Motorola 68000|68000-family]] exception fired:

{| class="wikitable"
|+ ''68000 / 68020 / 68030 exception subcodes''
! Subcode !! Exception !! Common causes
|-
| 0001 || Bus Error || Access to non-existent memory; failed RAM/ROM; bad address decoder. On a Plus or SE address references roll over rather than bus-error — seeing 0001 on those machines usually means a hardware fault rather than a software bug.
|-
| 0002 || Address Error || Word or long-word access at an odd address. Common when a bad CPU emits a partly-corrupt instruction stream.
|-
| 0003 || Illegal Instruction || CPU encountered an opcode it doesn't implement. Often a sign of corrupt ROM or RAM (especially in low memory where vectors live), or — on a 68000 — code intended for a 68020+.
|-
| 0004 || Zero Divide || Integer division by zero. Sometimes left in as a deliberate "you should never get here" trap by Apple's engineers.
|-
| 0005 || Check Instruction || {{code|CHK}} bounds check failed.
|-
| 0006 || TrapV / Overflow || {{code|TRAPV}} fired (arithmetic overflow).
|-
| 0007 || Privilege Violation || Supervisor-only instruction executed in user mode. The Macintosh runs in supervisor mode at startup, so seeing this very early is unusual.
|-
| 0008 || Trace || CPU was placed in trace mode without a debugger installed.
|-
| 0009 || Line 1010 / A-line || Trap-dispatch failure: the CPU saw a 1010-prefixed opcode (the [[A-trap]] mechanism Mac OS uses for ROM calls) but the dispatcher couldn't find it. Common when the OS image is corrupt or MacsBug / Easy Access traps are missing.
|-
| 000A || Line 1111 / F-line || Unimplemented F-line opcode — typically an [[FPU]] instruction on a machine without one (or with a removed/dead 68881 / 68882 / 68040 FPU).
|-
| 000B || Other exception / unassigned vector ||
|-
| 000C || Unimplemented trap / reserved ||
|-
| 000D || NMI (programmer's switch) || ''Normal indication.'' Generated when the user presses the Programmer's Switch before boot completes.
|-
| 000E || Spurious interrupt || Interrupt asserted but no slot/handler claimed it. Often a NuBus card with a failed interrupt line.
|-
| 000F || Trap-instruction vector || A {{code|TRAP #n}} fired without a handler.
|-
| 0040 (and 0041–0047) || Auto-vectors / interrupt-level traps || Interrupt level ''n'' fired without a handler (on '020+ machines line 1700+ is also used for these).
|-
| 0062 || Old-ROM reading [[HFS]] disk || A 64K-ROM machine ([[Macintosh 128K|128K]] / [[Macintosh 512K|512K]]) attempting to mount an HFS-formatted volume. The fix is either to format the boot disk as [[MFS]] or to upgrade to a 128K ROM (the upgrade that turns a 512K into a 512Ke).
|-
| 0064 || Couldn't read System File || ROM loaded enough of the boot blocks to start the OS but could not read the System file into RAM. Almost always a bad floppy or hard-disk error rather than a logic-board fault.
|-
| 0065 || Bad Finder || System loaded but the Finder is missing or corrupt.
|}

The original Apple Technical Information Library notes that on the [[Macintosh II|Mac II]] and later, the {{code|1700}}–{{code|1F00}} block of exception codes is used for FPU/PMMU exceptions; see [[#Macintosh Portable Diagnostic Codes|the Portable's expanded exception list]] below, which is the most complete published Apple-internal set of these.