Sw2 Switch Settings; Telemetry Line Termination (Sw2 1 E 2); Looping The Data Bus In Cat-5 Cables (Sw2 3 E 4) - Videotec MDI Manuel D'instructions

7.2 SW2 switch settings

Switch number
1 2
OFF OFF
ON ON

7.2.1 Telemetry line termination (SW2 1 e 2)

The bus architecture of RS-422 and RS-485 telemetry systems requires that the cabling originates at the
controller, passes through all domes and then terminates at the last dome with a 120 Ohm impedance.
To correctly terminate the telemetry cabling, place switches 1 and 2 in the ON position in the dome that is
physically the farthest from the telemetry transmitting device. Only the last dome is required to be terminated.
All other domes should have switches 1 and 2 in the OFF position. The factory default is OFF, OFF (un-
terminated).
Failure to correctly terminate the telemetry cabling may result in unreliable operation..
Please observe the limit for the number of devices that can be placed on a run of telemetry cabling. If unsure,
please consult the supplier of the telemetry controller.

7.2.2 Looping the data bus in CAT-5 cables (SW2 3 e 4)

Creating the right bus architecture normally necessitates running cabling from one dome to the next. This can
add extra cost because the telemetry cabling does not follow the "star" configuration of the video cabling of the
system. Simplex RS-422 and all RS-485 telemetry systems require just two conductors. This means that there
are two spare conductors in a system wired with CAT-5 cable. Switches 3 and 4 enable these spare conductors
to be used to loop the bus back to the start of the cable on these "spare conductors" where they can be more
easily joined to the conductors running to the next device. Table 9 shows the looped connections for both
simplex RS-422 and RS-485 telemetry wiring.
Telemetry
signal
Simplex RS-
422 +
Simplex RS-
422 -
RS-485 A
RS-485 B
NB: If you are going to use MACRO or Pelco D protocol (videotec keyboards and receivers) refer to
RS422 simplex communications where RS-422+ correspond to RS485A keyboard and
RS485 B.
3 4 5 6
OFF OFF
ON ON
OFF
ON
XX
Table 8 - SW2 switch settings
Data imput (from
previous dome)
Wire colour
Green/White
Green
Orange / White
Orange
Table 9 – CAT-5 cable with looped data-bus
7 8
Telemetry line termination
loop CAT-5 RS-485
Balanced video signal
Unbalanced video signal
No function
OFF OFF Local power supply
ON ON Remote power supply
keyboard or Looped output (to the next dome)
Pin No.RJ-45 Wire colour
3 Orange
6 Orange / White
1 Green
2 Green/White
Pag. 11
Function
All other domes
" Last dome in run
No loop
" Looped
CAT-5 o UTP
Coaxial cable
"CHAIN"
"CONTROLLER"
Pin No.RJ-45
2
1
6
3
RS422 – to
MNVCMDI_0419