Dxdp Communication - Panasonic KX-T7665NE Service Manual

10.7. DXDP COMMUNICATION

Function
This circuit performs the same communication as DXDP-compatible DPT and PBX
communication connected with DXDP port.
Circuit Operation
The data to Slave DPT is outputted from pin 33 and 34 of IC2 and sent by Transistor Q2 and Q3.
The data from Slave DPT is inputted to the comparator (pin 31) built in IC2.
The threshold voltage of the comparator is determined by R112 to 114 and inputted to pin 30
and 32 of IC2.
Also, the supplying power to Slave DPT is controlled by a constant current circuit of Q16 as
below.
- IC2-pin 28 as H : Constant current circuit ON
- IC2-pin 28 as L : Constant current circuit OFF
- IC2-pin 29 as H : 40mA Feeding (Slave DPT usually)
- IC2-pin 29 as L : 20mA Feeding (Slave DPT at starting up only)
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