Nellcor N-200 Operator's Manual page 61

One or more Z packets, each followed by a number of X and Y
packets. Each Z packet marks the beginning of an event period.
The number of X packets that follows each Z packet is given by
the first parameter Zn . . . n in the Z packet plus one. The very
last (Zn . . . n +1) packet sent is a guard packet (used for
spacing graphics output). The data in this last packet is invalid
and should be discarded.
Hence, Zn . . . n gives the number of valid X packets of data
points for each event period.
Thirty seconds (that is, 30 X packets) precede the first Y packet
marking the first event. There may be more events following,
each represented by a Y packet spaced among the X packets at
the time that the events occurred.
Command:
Device Sends:
N-200 Responds: < STX > V128< CRLF > < ETX > — Sent once
Note: The Y data packets may occur at any time during the
trend or event dump. The positions of the Y packets
indicate when the associated event occurred.
The host device must wait for a minimum of 30 seconds after
sending the V (stop sending) command before sending another
command.
< STX > E < CRLF > < ETX > — End of data,
normal completion
STOP SENDING
V < CRLF >
when command received.
Guide to Operation
55