AT&T 610 User Manual page 109

ESC[psn Terminal/Printer Status Request
Received Characters
Page 8-27
Receiving the sequence ESC[5n (terminal status request)
will cause the terminal to reply with ESC[On (test passed) or
ESC[3n (test failed).
Receiving the sequence ESC[?15n (printer status request)
will cause the terminal to reply with ESC[?lln (printer not
ready) or ESC[?lOn (printer ready).
ESC[psp Select Screen Labels
Receiving the sequence ESC[Op will cause the Sys Fkey
labels to become visible on the screen.
Receiving the sequence ESC[lp will cause the User Fkey
labels to appear.
Receiving the sequence ESC[2p will cause the Fkey labels to
be blanked.
Receiving the sequence ESC[3p will cause the PRINT Fkey
labels to become visible.
Receiving the sequence ESC[4p will cause the I/O Fkey
labels to become visible if there is an I/O card and it is being
used.
Receiving anyone of these sequences may change the LABELS
option (refer to Section 5).
ESC[psljpnjps2;ps3q Label String
Refer to Sectipns 5 and 6 for a description of this
sequence.