Manual OC32/NG
VPEB
Control your Miniature World
Page 22 of 48
Version 1.0 – December 15
th
, 2017
2017 Leon van Perlo
The RJ45 sockets are convenient if you use standard cables. You can use any standard,
straight RJ45 network cable you can find in a computer store. The 3-pole (green) wire end-
connector is convenient when you need to connect to something that has not an RJ45
RS485 connector or when you want to use your own cable.
Note:
There is no standard pin-out defined for RS485 on an RJ45 connector, so ‘the
standard’ is only guaranteed to work between VPEB products.
5.3.3
RS485 Termination
We receive quite some questions about ‘the RS485 terminators’. Apparently it is hard to
comprehend, while in essence the idea is very simple.
RS485 is one continuous wire-pair (the ‘bus’). There may, in principle, be no branches. On
‘the wire’ you can connect devices. So ‘the wire’ runs from module 1 to module 2 to module
3 to … to module N. It is important that ‘the wire’ is
‘terminated’ at both ends, so
the first and last module only
.
The OC32/NG provides terminator-jumpers so you can
activate and de-activate the termination function on the
module.
Note that there are two termination jumpers: TC1 and TD1.
Always activate or de-activate both. See figure 11.
See the whole setup as a laundry-wire. You have to fix
(terminate) the wire at both ends, otherwise it will fall, and
you can clip your shirts, socks and knickers at any point to
the wire.
5.3.4
Connecting to a PC via RS485
If you want to connect the OC32 to a PC, the best way to do is to use a U485 converter.
That is a highly compact USB-RS485 converter especially developed for the OC32. The
U485 is hardly more expensive than a standard USB-RS232 converter.
In its simplest form, the RS485 bus implementation consists of 2 modules with a cable
(twisted pair) in between: at one end a U485 and at the other end an OC32.
The RS485 is to be connected to pins 1,2 and 3 (labeled D+, D- en GND) of K2 (the 3-pin
connector). One wire of the twisted pair is connected to D+, the other wire to D-, a third
wire to GND. Because RS485 is polarity sensitive, you may not swap D+ en D-, so the wire
that is connected to D- has to be connected to D- at the other side as well. The same
counts for D+.
All connectors, both the one on the OC32 and on the U485 have the same pin layout, so pin
1 connects to 1, pin 2 to 2 and, if applicable, pin 3 to 3
The whole will look like the one below (figure 12):
Fig 11: Termination Jumpers
U485
RS485 terminators
activated
PC
RS485 terminator activated
Fig 12: PC to single OC32/NG
Control your Miniature World
VPEB
Manual OC32/NG
2017 Leon van Perlo
Version 1.0 – December 15
th
, 2017
Page 27 of 48
DCC Interface
DCC Low-
Pass Filter
•
Use a connection on which the data packets for Accessory decoders are generated. In
principle that is any connection but there might be exceptions with your digital system.
•
The load of an OC32 on the DCC interface is about 10..15 mA. It is that small that in
practice you seldom have to take this extra load into account.
With DCC a large number of modules (decoders) can be connected to the digital system. To
be able to control these decoders, DCC has an addressing method as well. The OC32 uses
up to 128 consecutive DCC accessory decoder addresses. The DCC start-address and the
amount of addresses used is set by means of software configuration (see OC32 firmware
manual), so
NOT
with dip-switches.
Fig 17: The DCC interface
The OC32/NG has both hardware and software filters to mitigate the effect of electrical
interference, voltage spikes, etc. Some users claim that the hardware low-pass filter on the
OC32 disturbs signal reception. We have found this is the case when an asymmetrical signal
is applied (so actually when the signal is not DCC compliant). If these problems are
encountered, the DCC Low-Pass filter on the OC32/NG can be disabled. As depicted in
figure 17, you’ll find a jumper JP8 (DCC-LPF). When the jumper is installed the Low-Pass
filter is enabled (standard), when the jumper is removed the Low-Pass filter is disabled (not
recommended unless you experience problems with the LPF enabled).
5.6
Additional Options
The OC32/NG has some additional options that are not available on a standard unit. If you
want to use these options, you have to make a small modification to the OC32/NG. The
reason for this is that these options are very rarely used and we don’t want to bother the
average user with yet another option to configure.
5.6.1
TTL Level serial input
The OC32 (original version) and the OM32 had the possibility to select TTL level input or
RS232 level input for the serial interface. The OC32/NG has two serial interfaces: RS485
