User guide

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The application drawings which follow show this process using
4051 8 channel multiplexers. It should be noted that the
analogue multiplex bus and the 4051's are all run at a 5V supply
in order to avoid converting the address and chip select signals
to CMOS voltages. This necessitates the potential divider at
the input for each channel, such that the 10V input can be
reduced in level. Components D1, D2 and R3 provide protection
against over voltage or reverse polarity inputs.
DMX512
Input
The DMX512 input connects directly to the output of a
standard RS485 or RS422 receiver such as the 75176.
Good Data
The GOOD signal is driven low to show that valid DMX512 data
is being received. The output is suitable for direct connection
(via a current limit resistor) to the cathode of a 20mA LED.
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
Analogue
Inputs
0 0 0 Analogue only Off On
0 0 1 Analogue & DMX Merge On On
5 1 2 Analogue & DMX Merge On On
7 0 1 Output 1 @ 100% Off Off
6 0 1 Output 1 @ 50% Off Off
7 6 9 Output 69 @ 100% Off Off
6 1 2 Output 12 @ 50% Off Off