Rane RPM 88 - Manual (Page 7)

Manual-5
fact, including the termination has proven to hinder the perfor-
mance of the RW 485 bus.
Five connection terminals are provided: a balanced pair of
data lines (A and B), a pair of power lines (±V), and a chassis
ground. All terminals should be connected to the corresponding
terminals of the Smart Remotes.
Up to 8 remotes, each having a unique address, can be con-
nected to the RPM 88. Any mix of SR 2, SR 3 and SR 4 remotes
is possible, as is any combination of star or daisy chain wiring
configurations.
The cable length limitations and the maximum number of
remotes that can be powered from the RPM 88 is limited by the
mix of remotes used, the cable type used, the distance to each re-
mote, and the wiring configuration. Detailed wiring and cabling
tables and several examples are discussed in the SR Manuals. A
Microsoft Excel Cable Length Calculator is downloadable from
the Rane website (go to the SR product pages).
The RW 485 port provides up to 280 mA of current, used to
power connected remotes. Each SR 3 remote requires approxi-
mately 90 mA, thus up to three SR 3 remotes can be powered
directly from the RPM 88.
Additional remotes may be powered using an external supply
(8 to 15 VDC regulated, minimum 0.8 amperes), leaving the +V
terminal of the RPM 88’s RW 485 port disconnected.
The RW 485 port is intended to be used with Rane’s Smart
Remotes only; we do not recommend directly interfacing the
RW 485 port with devices that are not compliant with the TIA/
EIA-485 standard, such as the “485” ports found on AMX and
Crestron devices.
Preset Recall Using Contact Closure Switches
The minimum “low” voltage required to detect a contact closure
and change Presets is 2.5 V. Since the internal pull up is 100 kΩ
to +5 V, it is possible to calculate the maximum allowable cable
length, provided the wire resistance per foot (or meter) is known.
Example:
To be safe, let’s allow a maximum of 80 kΩ worth of cable
resistance. This value keeps the voltage divider formed by the
100 kΩ internal resistance and 80 kΩ cable resistance from
dropping below 2.5 V.
(5 V * 100 kΩ) / (100 kΩ + 80 kΩ) = 2.777 V
If the cable resistance is 30 Ω per 1,000 feet
(1,000 feet / 30 Ω) * 80,000 Ω = 2,666,666 feet.
Thus, you can only use 2,666,666 feet (505 miles) of twisted
pair cable before the Preset recall functionality becomes inter-
mittent (assuming the cable is properly twisted and not run
through excessive magnetic or electric fields).
Remote Level Control Using Potentiometers
The VIP inherently prefers linear taper 10 kΩ potentiometers,
which provide a nice audio taper “feel” for the end user. When
used with suitable twisted pair wiring, the 10 kΩ value also of-
fers acceptable noise immunity and very long cable lengths.
Versatile Output Port (VOP)
Eight open collector logic output pins are provided, each capable
of sinking 100 mA of current. The on-board REF voltage of
12 VDC provides a maximum of 200 mA of current. Use an
external power supply (40 VDC maximum) if more current is
required, but be sure to connect the external supply’s ground to
the GND pin on the VOP.
RW 485 Port
The RW 485 port uses a simple, proprietary protocol to commu-
nicate with Rane’s optional Smart Remotes (SR 2, SR 3, SR 4).
The details of this protocol are found in each of the SR Manuals,
available from Rane’s website.
This port follows the electrical specification found in the
TIA/EIA-485 standard, with one exception: the recommended
termination impedance is neither implemented nor required,
since RW 485 uses a relatively slow baud rate (38,400 bps). In
pin 1
GND
Contact
Closure
20 kΩ (linear)
Level Control
Potentiometer
VIP CONNECTION
(examples for VIP pin 1)
GND
REF
pin 1
1N4001
+12
pin 1
2 kΩ
+12
pin 1
(examples for VOP pin 1)
VOP CONNECTION
Light an LED Relay Drive
100 mA coil
Crydom P/N D1225
current max
pin 1
+12
24 to
3
4
2
1
140 VAC
25 A max
Line Voltage Switching
NOTE: +12 VDC is available on the VOP. An external supply may be used as long as any VOP pin voltage never exeeds 40 VDC.
Examples shown are for 12 VDC only.