7700FR/7800FR MultiFrame
7800TR-32x24 Modular Tally Router
Page - 16
Revision 1.2
3.8
GENERAL PURPOSE I/O MODES
The 7800TR-32X24 tally router is designed to have flexible General Purpose I/O to allow them to be
used for a wide range of purposes such as illuminating lamps, and reading the state of switches. The
GPIs and GPOs can be hard-wired in Wet or Dry mode to interface with both powered and unpowered
devices using the provided WET voltage pins. The GPIs have a wide voltage range and high sensitivity
(see Table 3-5). The GPO relay contacts can support a relatively high current flow (see Table 3-6).
3.8.1 Tally Wet and Dry Terminology
The Tally Router is named after the most common use which is driving tally lights on cameras. In a live
recording studio with multiple cameras, each camera has a tally light which indicates it is the one that is
currently being broadcast. The director sends commands to switch between the cameras. The main
video router switches the video feed between the cameras, and the tally router follows by switching the
corresponding tally light GPOs.
Throughout this manual the “wet” and “dry” terminology is used to describe whether a GPO and GPI
provides/requires an external voltage source to operate. This terminology is arcane and confusing
outside its narrow scope of usage. The term “Wet” means that voltage is present and “Dry” means no
voltage,
always from the perspective of the output port
(General Purpose Output).
When connecting a GPO to a GPI, remember “
Wet
” to “
Wet
” and “
Dry
” to “
Dry
”.
Never connect “
Wet
” to “
Dry
” or vice-versa.
A General Purpose Output has two contacts marked “A” and “B”. A “Dry” GPO opens these two
contacts when OFF, and closes them when turned ON. No voltage is supplied. A “Wet” GPO provides
+WET
voltage when it is activated in order to provide power to a downstream device such as a light
bulb, buzzer, or Wet GPI. See section 3.6 for more information.
A “
Wet
” GPO
provides
voltage to the downstream device.
A “
Dry
” GPO
does not provide
voltage to the downstream device.
The General Purpose Inputs are used to read the state of another device. This may be a passive
device such as a pushbutton or switch, but is often connected to a GPO. A “Wet” GPI is named such
that it is wired to connect to a “Wet” GPO. This means a “Wet” GPI does not provide its own voltage
source. A “Dry” GPI is meant to interface to a “Dry” GPO. This means that it provides a
+WET
voltage
which the external device must return in order to activate the GPI. See section 3.5 for more
information.
A “
Wet
” GPI
requires
an external voltage to be applied in order to activate it.
A “
Dry
” GPI
requires
only an external contact closure to return its own voltage to activate it
