User`s guide

The timeout facility is not ordinarily enabled when the printer is in
interactive mode.
Auto Select and Emulation Timeouts
The other two modes of communication, emulation and ESP, also
have timeouts associated with them. They are
emulation
wait
Default for this timeout is 5 seconds. The emulation
wait timeout limits the time the printer waits for more
data on a job already in progress. It is only supported
for emulations (for example, HP PCL), not PostScript.
autoselect
wait
Default for this timeout is an integer value 3 seconds.
The autoselect wait timeout limits the time the printer
waits before trying to select the proper language. This
period is ignored if 256 bytes of data are received before
3 seconds expires. It is only supported when the
interface is in ESP mode.
Manual Feed Notes
If manual feed is invoked (by setting manualfeed to be true in
statusdict) too quickly after printing a previous page using normal
feed (from the paper tray), the printer mechanism ignores the
request to use manual feed. To avoid this problem, when switching
from normal to manual feed, be sure at least 5 seconds elapse before
issuing the next showpage. If necessary, insert a delay explicitly
by executing the statement
usertime 5000 add
{dup usertime lt {pop exit} if} loop
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Chapter 9
9-12 PostScript: Technical Overview