mp-tray

Returns or changes the value of the multi-purpose (MP)
tray configuration variable.  The MP tray can be
configured to operate as an additional input tray
(eCassette), a manual feed slot (eManual), or in a
manner compatible with the LaserJet III manual feed slot
(eFirst).  If configured for eFirst, if media is present
in the MP tray, that media is used (assuming the size
matches and the print job didn't specify another tray)
until the MP tray is empty.
Additional information:
The MP tray can be configured for use either as a paper
cassette or as a priority manual feed tray.  When the tray is configured as a manual feed tray, unsolicited status messages are not generated when there is no 
paper in the tray.  LaserJet 4050 Series will pull media from TRAY 1 only if there is
a sheet present and it matches the needed size and type.

MIB

HP-LASERJET-COMMON-MIB

OID

.1.3.6.1.4.1.11.2.3.9.4.2.1.4.1.3.1.5

Type

scalar

Access

readwrite

Status

mandatory

Parent

settings-intray