Specifications

SB-P-06-4066
sepura
Mobile & Gateway Accessory i/f
specification
30th July 2012
Page 24 of 39
Issue 7c
© Sepura plc 2011
Accessory ID resistor
Microphone resistance
Gain setting
≥ 10 kΩ
> 1 kΩ, e.g., electret
―Normal‖
≥ 10 kΩ
< 100 Ω, e.g., moving
coil (AIU Mk2)
―High‖
0 Ω
any value
―High‖
5. The earpiece amplifier does not have any output current limiting resistors fitted and is
designed to drive loads with a minimum impedance of 8 Ω loads from a 5 V supply
6. The transceiver mutes the microphone by turning off the electret microphone DC
supply on pin 7 of the AAI. If the audio source is not an electret microphone, then the
accessory must implement its own mute by detecting the loss of the DC voltage from
this pin.
7. When Normal gain is selected, the presence of a microphone load with a resistance
of less than 100 Ohms will automatically select a higher gain signal path. This
functionality is intended to allow dynamic microphones to operate with this interface -
as used in certain motorcycle helmet installations. The transceiver is unaware of any
gain change.
8. These signals and pin out are not compatible with SRM1000 accessories.
AUDIO ACCESSORY IDENTITY TABLE
The transceiver identifies audio accessories attached to an AAI through the resistance
presented between pin 1 and pin 2 of each AAI.
Audio Accessory Type
Associated identifying
resistor value, ohms
(2%)
Nominal
voltage on
ACC_ID pin, V
Nominal
ADC value
no device attached

5
255
reserved
220k
4.1
210
local microphone, PTT & hook, (e.g. fist
microphone)
100k
3.4
173
local microphone, PTT, earpiece & hook
(e.g. handset);
47k
2.5
128
local microphone & PTT without hook
(e.g. desk microphone)
22k
1.6
82
local microphone, PTT & earpiece without
hook (e.g. headset)
10k
0.88
45
remote microphone & switches without
hook;
0
0
0
ACCESSORY KEYS TABLE
The transceiver identifies which accessory key is pressed through the resistance presented
between pin 4 and pin 2 of each AAI.