Panasonic KX-MB771GR Service Manual page 109

KX-MB771GR
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 300-G23pin. (NHSYNC)
Note:
As for the "Pulse" waveform of the above flow chart, see the timing chart.
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