Panasonic KX-FLB802CX Service Manual page 122

KX-FLB802CX/KX-FLB812CX/KX-FLB802CXS/KX-FLB812CXS
12.3.6.2. CALL SERVICE 2
"CALL SERVICE 2" means that the synchronous signal out of the LSU cannot be detected.
The synchronous signal out of the LSU is detected by IC 604-59pin. (XHSYNC)
Note:
As for the "Pulse" waveform of the above flow chart, see the timing chart.
122