AVS-1210
I.R.T. Communications Pty Ltd | www.irtcommunications.com
Revision 06
Control circuit
Control logic is performed by a Programmable Logic Array (PLA) which has been programmed for the required
operations. This component will only function correctly when loaded with the correct program and is therefore
only available through IRT.
The switcher has two control connectors on the PCB that normally connect direct to corresponding connectors on
the rear panel.
They are labelled PL 4 and PL 5. For descriptive purposes, PL 4 is called the “input” connector and PL 5 the “output”
connector.
The pins on these connectors have the following functions:
PL 4
PL 5
1A
+12 Vdc
NC
1B
Ground
Ground
2A
Data 4
Data 4
2B
Data 3
Data 3
3A
Data 2
Data 2
3B
Data 1
Data 1
4A
Data 0
Data 0
4B
Switch pulse in
Switch pulse out
5A
Busy out
Busy in
5B
Unlatch in
Unlatch out
The 5 bit codes on Pins 2A to 4A represent the input selected. This code is in BCD (Binary Coded Decimal) where
the Data 0 to 3 represent the binary numbers 0 to 9 (Inputs 1 to 10 if Data 4 is 0 or Inputs 11 to 20 if Data 4 is 1).
The
unlatch out
signal is asserted by a switcher if any of its front panel switches is operated or if its
unlatch in
signal is asserted. The presence of an
unlatch in
signal causes any switcher to release control of the data lines (if it
had control of them).
A switcher signals that it has control of the data lines by asserting
busy out
.
Busy out
also ripples
busy in
.
The operation of a push-button ripples unlatch to modules farther down the chain, causing any of them with
control of the bus to release it, and in so doing clear the
busy
line.
As soon as the requesting module sees its
busy in
line clear, it takes control of the bus and asserts its
busy out
. The
busy out
signal then ripples up the chain causing any other modules release control (if they had it).
1B 2B 3B
4B 5B
1A
2A
3A
4A
5A
