HP Color LaserJet 5500 Technical Reference Manual page 256

Paper Tray
Configuration
A-44 Feature Support
5. The software may resume sending data after it sees the
printer go back online.
6. If the software does not detect the printer going offline
and then back online within 5 seconds of the echo, the
application may assume there is a printer error.
The LaserJet 4000 series paper tray configurations are set
up as follows:
Tray Number
0
1
2
4
x
Other trays are dynamically assigned at power-up, based on
the tray's number (for example, if you have a LaserJet 4000
series printer with an optional tray, tray 1 (MP tray) would
be 0, the first cassette number 2, the second cassette
number 3, and the optional cassette number 5 (number 4 is
reserved for the envelope feeder).
Description
Multi-purpose tray
Manual feed tray
Unknown tray
Envelope feeder
Other trays (see below)