4 Most significant channel select (CS3)
5 + 8 to 20 VDC input
6 Carrier detect output (pulls to 3.3 VDC through internal 1000 ohms)
7 Auxilary input
8 Auxilary ouput
9 Auxilary control PIN
10 Microphone input
Volume control (RSSI option)
11 DC output (5V)
Auxilary monitor input (pull to ground to open squelch). Can be used for tone detect, see below.
12 Red LED control
13 Green LED control Speaker output
13 Carrier detect output (pulls to 3.3 VDC through internal 390 ohms)
14 Reserved
15 Ground
16 PTT (pull to ground to transmit)
17 PC programing port
18 PC programing port
19 S
20 Speaker -
