Editing Sad Mac Error Codes (section)

== Test Manager (Serial Diagnostic Mode) ==

: ''Main article: [[Diagnostic Serial Console]]''

Every Macintosh from the [[Macintosh SE|SE]] onwards exposes a hidden Test Manager over the modem-port SCC. Connect a null modem cable from the modem port to a host running a serial terminal at 9600 8N1, then send a {{code|*}} to interrupt whatever the machine is doing and enter Test Manager. The trap {{code|_TestManager}} (defined in the same ROMs) provides the same interface programmatically.

Once inside, single-character commands followed by hex arguments and a {{code|*R}} (return / run) drive any test in the table. The two most useful for board-level diagnosis are:

* '''Per-test execution''' — {{code|*T<TT>0001<minor>}} runs test {{code|TT}} once and returns its result on the next line. Example: {{code|*T000400010000}} runs test 04 (RAM Bank A) once.
* '''Per-ROM checksum''' — {{code|*T000400010000}} on a IIcx/IIci/SE/30 will (because test 04 also covers the four-chip ROM array on those machines) return {{code|R<class><result>0000}} where the result narrows the failure to one of the four physical ROM chips ({{code|0001}}, {{code|0002}}, {{code|0004}}, {{code|0008}}).

The same interface is used by Apple's internal MacTest / MacTest Pro / Apple Personal Diagnostics suites. Note that some test commands (notably the full SCSI test) will hang a machine that has a non-functional SCSI chip — be ready to power-cycle.