I.S. INTERCOM
20-278-12
TYPE ABMA4 USER MANUAL
6 OF 21
Issue: 05
2. OPERATIONAL DESCRIPTION
The intercom type ABMA4 has seven front panel mounted push buttons. The main visual difference between
the ABMA4 and other I.S. Intercoms is that the ABMA4 has a LCD graphical display and addition of ‘Menu’,
‘Enter’, ‘Up’ and ‘Down’ keys or push buttons (‘keys’ will be used interchangeably with ‘push buttons’
throughout this document). Another difference is that the ABMA4 has a more powerful micro controller that
allows graphical representation of the state of cable, PSA controller and internal operation of ABMA4.
Photograph 4: ABAM4 Menu Keys
There are three main areas showing the working of ABMA4:
1. Background Operations
2. LCD Generic Graphical Display Mode
3. Configuration and Status Mode
3. BACKGROUND OPERATIONS
These tasks happen no matter what state the graphical display is at. These are as follows:
1. Detection of PSA (Pre-Start Alarm)
2. Detection of Speech for Speaker Mute Control
3. Detection of Low R-Line Voltage
4. Pressing of SPEAK key
5. Switching between Sleep and Deep Sleep modes
6. Watchdog kicks
1. Detection of PSA
The unit continuously detects for a PSA paired tone signal on both the V-line and S-line. The V-line is the
audio signal from the PSA Controller and the S-line is a return signal from end termination unit or Tail End
Unit (TEU). TEU (such as TEU100) returns the signal with the tone frequency divided by eight. The following
frequency pairs are detected on the V-line:
1. 1500Hz alternating with 1800Hz @ 0.4mS cadence
2. 1400Hz alternating with 1700Hz @ 0.2mS cadence
3. 1300Hz alternating with 1900Hz @ 0.8mS cadence
The AMBA4 units check for cadence as well as frequency tones pair for a PSA confirmation. The cadence
period need to be present for at least three quarters of the cadence for each frequency pairs for detection.
For example, a 1500Hz and 1700Hz is an in-correct pair. The frequency and cadence ensures a false PSA