NEC IE-784000-R User Manual page 76

(1) Mode
The mode is fixed to the modem mode.
(2) Setting of FG
The FG select jumper (JP3) is used for setting of FG. When this jumper is set to the FG (frame ground) side,
FG is opened. When it is set to the SG (signal ground) side, FG and SG are shared.
Usually, set the jumper to the FG side (open).
76
CHAPTER 8 FUNCTIONS OF RESPECTIVE CHANNELS
Fig. 8-1 Circuit Diagram of FG Select Jumper (CH1)
FG of CH1
FG SG