User guide

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TL084 has been chosen in order to provide a very high input
impedance for the sample and hold circuit.
It should be noted that the address and chip select signals
are all converted to CMOS voltages, in order to drive the
demultiplex circuitry at a 15V supply.
The analogue output of the DAC is amplified to produce the
analogue level required by the demultiplexors.
DMX512
Base
Address
The BCD inputs are used to set the DMX base address. The
inputs are set up for connection of three standard Binary
Coded Decimal Thumbwheel switches. The BCD inputs are
active low, i.e. to select a base address of 001, connect UNIT1
to ground and pull up all other BCD inputs. Valid addresses
range from 001 to 512.
Test Mode
The BCD inputs are also used to enter test mode.
When Test mode is active, the DMX512 input is disabled.
When the Hundred inputs are set to either ‘6’ or ‘7’ Test mode
is active. The Hundred input sets the intensity, while the Ten
and Units inputs select the channel.
The following examples show the operation:
Hundreds Tens Units Output DMX
Input
0 0 0 All Off Off
0 0 1 Controlled by inputs On
5 1 2 Controlled by inputs On
7 0 1 Output 1 @ 100% Off
6 0 1 Output 1 @ 50% Off
7 6 9 Output 69 @ 100% Off
6 1 2 Output 12 @ 50% Off