Grass Valley 2000NET v4.0.0 - Manual (Page 72)

72 2000NET Instruction Manual
Functional Description
Frame Bus
The Frame Bus provides serial communication to each of the media
modules for remote configuration and monitoring over a network.
Multiplexer and A/D Converter
The Multiplexer and A-to-D converter circuit is used to read the following
lines:
• Media Module Present Lines (12 front media modules, 12 rear media
modules)
• Center module preset lines
• Power Supply/Fan Slots Module Preset
• Frame Version
• Frame Type
• Fan Rotation
• Front Panel Fault/Presence
• Power Supply Health
The circuitry consists of five multiplexers, an A/D converter, and miscella-
neous passive circuitry. The processor selects the line to read then drives
the multiplexer to select a particular input of that multiplexer. The pro-
cessor then waits a fixed amount of time for the circuit to settle and then
reads the level using the A/D converter. Most of the input lines are con-
nected to ground through a resistor.
This circuit also has protection on most inputs. A 1 k¾ resistor and diodes
clamp each input (except fan rotation) to 3.3 V to prevent a bad input from
causing the whole circuit to fail.
The processor should get a value of between 2.1 V and 2.7 V when reading
power supply health.
Fan Rotation Sensor
The fan rotation circuit consists of a multiplexer and a one-shot IC followed
by an RC filter. The multiplexer is used to select one of the eight possible
fan rotation lines. When connected to a fan, these lines carry a square wave
with a frequency proportional to the fan speed. The one-shot circuit pro-
duces a DC output proportional to the frequency of the square wave. This
circuit requires about 1 second to settle once one of the lines is selected. The
fans used in the 2000 series frame have a rotation sense period of approxi-
mately 3.4 ms.