Connector Pin Assignments Pin No. Name Description 1 PTT Push to talk, open collector output to radio transmitter, maximum off state voltage 45V, maximum on state current 0.75 amps 2 GPIO1 General purpose input or output (note 1) 3 GPIO2 General purpose input or output (note 1) 4 GPIO4 General purpose input or output (note 1) 5 GPIO5 General purpose input or output (note 1) 6 GPIO6 General purpose input or output (note 1) 7 CTCSS_DET Input, diode isolated, continuous tone-coded squelch system detect (note 2) 8 COR_DET Input, diode isolated, receive (carrier operated relay) detect (note 2) 9 MIC_IN Direct low-level audio input to CM119, must be AC coupled (note 3) 10 GPIO7 General purpose input or output (note 1) 11 GPIO8 General purpose input or output (note 1) 12 AOUT AC coupled output from 6dB gain amplifier 13 GND Ground 14 +5V 5 volts DC power output from USB bus 15 EEP_CS EEPROM chip select control 16 EEP_CK EEPROM serial clock 17 EEP_DI EEPROM data input 18 EEP_DO EEPROM data output 19 GND Ground 20 GND Ground 21 MIC_AC Audio input, line level, AC coupled 22 LEFT_OUT AC coupled left audio output, 4KHz bandwidth 23 RIGHT_OUT AC coupled right audio output, 4KHz bandwidth 24 AIN AC coupled input to 6dB gain amplifier 25 AVDD 12 volt DC power input required for 6dB gain amplifier Note 1: Absolute maximum voltage on all GPIO lines is from -0.3 to 5.5V. Maximum current is ±8mA. Note 2: Absolute maximum voltage on CTCSS and COR is -0.3 to 40V. Maximum current is ±4mA. Note 3: Absolute maximum voltage on MIC_IN is from -0.3 to 5.5V. The URI radio interface connector is a standard female 25-pin D-shell COR/CTCSS. These two inputs are diode isolated and require an external pull-up resistor. A logic high must be between 3.5 and 40 volts. A logic low must be between -0.3 and +0.3 volts. 3