Grass Valley XtenDD DD - Manual (Page 129)

6. Tally Signalling
6 - 11 Planning and Installation - Rev. 3 / 04.2005
6.7 DESCRIPTION MI-3040 TALLY BOX
Reset
Gen.
Osc.
3.6864MHz
RESET
68HC705
PORT A
PORT B
PORT B
RS-422
Driver/Receiver
TO MPK
40
Opto-
Isolators
40
Relays
Relay
Interface
LCA
MI-3040R
Optical status
interface
LCA
MI-3040S
Data/Address Bus
Control
The MI-3040 interface performs two functions. It provides 40 switch closures and
monitors 40 isolated status inputs. It interfaces with a HD35 using MPK protocol.
The relay selected for this design is an optically-coupled solid-state relay
(PVD1352 by International Rectifier) capable of switching from 0 to 100 volts (AC
or DC) at up to 300 mA. Each relay may be configured by slide switch for normally-
open or normally-closed operation.
Each relay drive signal passes through a two-input exclusive-OR gate. The second
input to each gate is tied to a DIP switch to ground and pull-up. When a switch is
in the OPEN or OFF position, the corresponding relay is considered normally open;
a high level on the relay drive line (inverted to a low level) will consequently close
the relay. Conversely, when a switch is in the CLOSED or ON position, the corre-
sponding relay is considered normally closed; a high level on the relay control line
will cause this relay to open.
The opto-coupler inputs respond to a differential voltage between the two input
pins. The opto-couplers selected for this design are a bipolar type (PC314 by
Sharp, for example) to eliminate the need for external steering diodes. The signal
leg contains a series current-limiting resistor selected to provide between 1.75 and
13.6 milliamps of LED drive current at voltages of 5 to 28 volts (AC or DC).
Block Diagram
Optoelectronic
relays
Relay Control
Opto-couplers