SLR5500 Auxiliary Connector

I've had a few questions about connecting peripheral equipment - such as repeater controllers and data terminals - to the SLR5500 repeater. In all cases, this equipment needs to connect to the auxiliary connector on the back (shown above).

This is a standard 25-pin D-subminiature female connector. The matching plug is available from any electronics store.

Most of the questions I've been asked relate to which pins one get get various signals from, so here is a listing:

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Pin	Function	Comment
1	TX Audio	80mV for 60% RSD. Z=600Ω @1kHz
2	GPIO1	Configurable TTL IO*
3	NU	Not Used
4	GPIO2	Configurable TTL IO*
5	GPIO10	Configurable TTL IO*
6	GPIO9	Configurable TTL IO*
7	RX Audio	330mV @ 60% RSD & 1kHz Z=1kΩ
8	GPIO6	Configurable TTL IO*
9	Ground
10	GPIO7	Configurable TTL IO*
11	GPIO11	Configurable TTL IO*
12	GPIO12	Configurable TTL IO*
13	TX Data	80mV for 20% RSD. Z=600Ω
14	NU	Not Used
15	GPIO3	Configurable TTL IO*
16	Ground
17	Ground
18	Ground
19	Ground
20	Fused B+	13,6Vdc nominal 1A max.
21	GPIO8	Configurable TTL IO*
22	TX Audio	80mV for 60% RSD. Z=600Ω @1kHz
23	GPIO4	Configurable TTL IO*
24	GPIO5	Configurable TTL IO*
25	NU	Not Used

In case you need it, here is the pin layout for the matching plug as seen from the solder side:

The GPIO pins are TTL level digital input/outputs. They can be configured to be an input or output based on the chosen function. When set up as an input, it's basically the base of a transistor with a 4,7kΩ resistor to ground. When set up as an output, it's an open collector of a transistor pulled to an internally sourced 5V line. You cannot drive anything more than 1mA from them so if you're wanting to control bigger stuff, you will need some interface electronics.

The following functions are available:

• AC Power failure. This pin will go active whenever mains power is lost. There is a primary DC power setting in the CPS that, when enabled, will prevent this output from going active.
• Antenna Relay
• Channel Select. This input will allow you to change channels in the repeater by applying a BCD value on up to five Channel Select inputs. Have a look here for more details.
• CSQ Detect. This pin will go active whenever carrier is detected.
• Disable. This is an input line, that when activated, disables the repeater. When changing state, the repeater will perform a reset.
• External PTT. As the name suggests, this is a PTT input.
• FCC Type 2 Monitor. This is an input line, that when activated, prevents the repeater from keying up and from repeating inbound calls in a IP Site Connect system.
• Football Knockdown. This is an input line, that when activated, disables the receive and transmit operation of the repeater for as long as the pin is activated. CWID will not be transmitted while this input is active (applicable to Single Site Digital Repeater mode only).
• Major Alarm. This output will go active whenever a major alarm is detected in the hardware. Some alarms can be set to major or minor in the CPS/RM. Generally, a major alarm is anything that will cause the repeater to malfunction. A reset is usually needed to clear alarms of this type.
• Minor Alarm. This output will go active whenever a minor alarm is detected in the hardware. Some alarms can be set to major or minor in the CPS/RM.
• Monitor. When this input is activated, the receiver squelch will be disabled. Applicable to analogue repeater mode only.
• PL/Talkgroup Detect. In analogue mode, this output will become active whenever CTCSS is detected. In digital mode, this output will go high whenever a talkgroup call is present on either timeslot.
• Repeater Knockdown. When this is an input is activated, the internal repeat path of the repeater will be disabled. An external device can then control when the repeater keys-up. Applicable to Analogue Repeater mode only).
• Reset. Triggering this input will make the repeater carry out a reset.
• Site Slot Sync Input. Used for MOTOTRBO Link.
• Site Slot Sync Output. Used for MOTOTRBO Link.
• TX PL Inhibit. When active, this is input will inhibit the transmission of CTCSS/DCS whenever the repeater transmits. Applicable to analogue repeater mode only.
• TX Power High. When this input is active the repeater will transmit using the CPS programmed high power setting - if the current channel is set to low power.
• Unassigned. The GPIO has no function assigned to it.

Each GPIO has an active level. When setup as an input, this can be active low (0 to 0,8V) or active high (3,3 to 5V). When setup as an output, the output transistor will be pulled low (ca. 0,7V) or high (ca. 5V).

TX data on pin 13 is to be used for repeater controllers that generate CTCSS or DCS on a seperate output (i.e. audio and signaling are summed in the repeater).

The Fused B+ output can be used to power things like repeater controllers; trunking controllers or low power single-board computers.

The voltages shown in the table are RMS.

Some things to think about...

Whenever connecting external equipment to this connector, its important to consider galvanic separation. For GPIOs I prefer to use optocouplers. For audio lines, I try to keep cable runs short (less than a meter) and will always use shielded connectors and cables. 

If using the audio lines, the external equipment must source power from the same mains line and careful attention must be paid to floating and net neutral.

Bringing anything from outside the room/building into the AUX connector is a big no-no in terms of R56.