CDM index
Motorola index
Back to Home
  Motorola CDM-series
Mobile Radio
Accessory Connector

By Robert W. Meister WA1MIK
  Print this Page

The CDM-series mobile radios use a 20-pin accessory connector. The middle 16 pins will accept the standard MaxTrac/Radius/GM300 16-pin accessory connector. The same physical contact pins are used. Some of the pins have the same signals on both radio series; these are listed in the "Eq" column. Pin numbers and signal names in square brackets are defaults or suggested alternatives. The programmable Digital Input and Output pins are terminated with some resistance to ground or a supply voltage. Pins programmed as outputs are driven low by transistors that pull to ground. None can actively pull up.

Unlike the MaxTrac/Radius/GM300, you don't need any jumpers installed on the accessory connector to make the radio operate with the internal speaker. In fact, you don't even need to plug in an accessory connector at all.

Accessory Connector Pin Assignments:

PinEqSignal NameTermination
11 Speaker Output (Negative) 
22 External Microphone Audio Input 
3[3] Digital Input 1 [PTT]4.7k to 5V & 47k to Gnd
44 Digital Output 24.7k to 12V
55 Flat TX Audio Input 
66 Digital Input 310k to 5V
77 Ground 
88 Digital Input/Output 44.7k to 5V
9[9] Digital Input 5 with Wakeup [Emergency]47k to 5V
1010 Digital Input 6 with Wakeup (Ignition)4.7k to Gnd
1111 Flat/Filtered RX Audio Output 
1212 Digital Input/Output 74.7k to 5V
1313 Switched B+ 
1414 Digital Input/Output 84.7k to 5V
15No RSSI 
1616 Speaker Output (Positive) 
17--- BUS + (Programming/SCI+) 
18--- Boot Control 
19--- N. C. 
20--- N. C. 

Notes About Specific Pins:

On my CDM1250, when pin 7 is jumpered to pin 9 and power is applied to the radio, the radio turns on automatically. This may be the meaning of "with Wakeup". Without this jumper, I needed to press the front panel VOL knob to turn the radio on.

Pin 10 may be used for Ignition Control. You must supply +12V to this pin to turn the radio on, and of course program the radio to use Ignition Control. There are no internal jumpers or fuses to deal with, as with the MaxTrac etc.

On my radio, pin 11 (RX Audio Output) was producing filtered (de-emphasized) and muted audio. With a 400 Hz tone deviated at 3 kHz on a wideband channel I measured 1.88VAC, or about 0.63VAC per kHz of deviation with a 400 Hz tone. The level followed the standard 6dB/octave de-emphasis curve, however it started limiting slightly at 4 kHz of deviation. The graph below shows the output voltage.


On my radio, pin 15 (RSSI) went from 0.8VDC with no signal to 2.4VDC with the strongest signal. The graph below shows this voltage.


Accessory Connector Orientation:

The diagram below was extracted from the Detailed Service Manual. Note that the locking tab for the accessory plug is on the bottom edge of the connector, which is closest to the bottom of the radio when looking at it from the rear.


Digital (Programmable) Input and Output Pins:

On my CDM1250, pin 10 is not listed as being programmable; it's always Ignition. That might be different on the CDM750 or CDM1550. Pin 9 can only be programmed for Null or External Emergency Switch (Input). All the other pins (3, 4, 6, 8, 12, 14) can have the following functions assigned to them, depending on whether they are Input, Output, or Input/Output. The pins can be active high or active low, and on the input pins, with or without Debounce. The lists below have been sorted alphabetically; the choices will be in a different order when viewed via CPS.

Input Signal Selections:

Channel Select 1
Channel Select 2
Channel Select 3
Channel Select 4
Data PTT
Data Revert
Emergency Input
External Call Button 1
External Call Button 2
External Mic. PTT (Default for Pin 3)
LS RPTR Control
Mic. Off Hook
Null (No Function or Purpose Assigned)
Option Board 1
Option Board 2
Option Board 3
Option Board 4
PA Switch
Request To Send
Rx Audio Mute
Special Off Hook
TOC Disable
Tx PL Inhibit

Output Signal Selections:

Auxiliary Control 1
Auxiliary Control 2
Clear To Send
CSQ Detect
External Alarm
Null (No Function or Purpose Assigned)
Option Board 1
Option Board 2
Option Board 3
Option Board 4
PL and CSQ Detect/Talkgroup Detect

Acknowledgements and Credits:

The diagram of the accessory connector came from the CDM and PRO Detailed Service Manual, p/n 6881091C63-O.

Signal Assignment information came from Professional Radio CPS Version R06.12.09.

16- and 20-pin connectors and kits can be purchased on ebay from seller mre1032.

Contact Information:

The author can be contacted at: his-callsign [ at ] comcast [ dot ] net.

Back to the top of the page
Up one level (CDM index)
Up two levels (Motorola index)
Back to Home

This page created on Saturday 08-Oct-2016.

Article text, artistic layout, and hand-coded HTML © Copyright 2016 by Robert W. Meister WA1MIK.

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.