AT&T 6300 Programmer's Manual page 251

Syntax
Example
ERDEV and ERDEV$
Functions
ERDEV is an integer function which contains
the error code returned by the last device to
declare an error.
ERDEV$ is a string function which contains
the name of the device driver which generated
the error.
[ ERDEV
I
ERDEV$ ]
ERDEV is set by the Interrupt X'24' handler,
when an error within MS-DOS is detected.
ERDEV will contain the INT 24 error code in
the lower 8 bits, and the upper 8 bits will
contain the "Word attribute bits" (b15-b13)
from the Device header block. If the error was
on a character device, ERDEV$ will contain
the 8-byte character device name.
If the error was not on a character device,
ERDEV$ will contain the two character block
device name (A:, B:, C: etc).
User installed device driver "MYLPT2" caused
a "Printer out of Paper" error via INT 24.
If the driver's error number for that problem
was 9, ERDEV contains the error number 9 in
the lower 8 bits and the device header word
attributes in the upper 8 hjts.
ERDEVS contains "MYLPT2."
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