FOCUS Enhancements 3.2 - Manual (Page 162)

External Control Commands
148
Still (ST)
Command:
Pauses the current file position and freezes the picture.
Format:
ST
Response:
R
Explanation:
ST is treated exactly the same as PA except that instead of the
video output going black, the current video frame is held on screen.
If an ST command is received after a PA the effect will simply be
to unmute the video output. Likewise, if a PA is received after an
ST, the effect will simply be to mute the video.
Examples:
ST
Pauses the Firefly and freezes the current frame on each video
output.
0@ST
Pauses the Firefly and freezes the current frame video output.