4081 User Manual
Issue 3
USB / RS 485
It is possible to 'daisy-chain' multiple units together so they are controlled
via USB on a Mac or PC.
The first unit on the chain should be connected to the Mac or PC by a USB
cable (not supplied).
The blue USB/RS485 button on the rear of this first unit should be
pushed in to select USB.
Subsequent units are connected from the RS 485 OUT of the 1
st
unit, to
the IN on the 2
nd
; from the OUT of the 2nd to the IN of the 3rd and so on
(these subsequent units should all have the blue USB/RS485 button on
the rear pushed out to select RS485 control).
The RS 485 communication protocol uses RJ9 connectors for connecting
cables where multiple units can be chained together, going from OUT to
IN as described above (cabling not supplied).
NB:
This cable should be wired pin-to-pin.
Please note that when connecting multiple units, each 4081 should have a
unique ID as shown left.
The procedure for setting these IDs is described on page 29.
Cable Specification
The RS-422 specification recommends 24AWG twisted pair cable with a
shunt capacitance of 16 pF per foot and 100 ohm characteristic
impedance.
These recommendations should be used for RS485 systems as well.
We also recommend using shielded cable.
There are many cables available meeting the recommendations of RS-485
made specifically for this application. Another choice is the same cable
commonly used in the twisted pair Ethernet cabling. This cable, commonly
referred to as Category 5 cable, is defined by the EIA/TIA/ANSI 568
specification.
This cable has a maximum capacitance of 17 pF/ft (14.5 pF typical) and
characteristic impedance of 100 ohms.
Category 5 cable is available as shielded twisted pair (STP) as well as
unshielded twisted pair (UTP) and generally exceeds the recommendations
for RS-422 making it an excellent choice for RS-422 and RS-485 systems.
- 27 -
Standalone Mac / PC or DAW
USB cable
ID 1
RS485 cable
ID 2
RS485 cable
ID 3
RS485 cable
etc....
