AN2677/D
2 Digital Satellite Equipment Control (DiSEqC ) using MC68HC908QT/QY
DiSEqC Introduction
The DiSEqC standard is a single master, single or multiple slave system, so
communications may be initiated only by the master tuner-receiver/IRD. The
The slave devices can be switches, LNBs (low noise blocks), positioners, or
other special devices used to establish satellite program reception.
The bus transfers:
– dc power supply — usually 13-V/18-V; max 500 mA
– RF signal — IF band from 950 MHz to 2150 MHz
– 22-kHz tone signal — nominal 650 mV (± 250 mV) peak-to-peak
– DiSEqC data modulated on the 22-kHz tone signal (if used)
To help ensure the transport of the 22-kHz signal, the total load capacitance of
the entire bus (cable) should not exceed 250 nF. At this load, the bus can
tolerate a cable as long as 50 meters. DiSEqC peripherals should not load the
bus by typically more than 100 nF. For certain classes of devices such as
SMATV (satellite master antenna television) nodes and installer aids, a much
lower value is preferred.
DiSEqC
Signal/Protocol
See the DiSEqC bus specification from http://www.eutelsat.com for complete
bus specification.
There are several signal possibilities on the bus:
• Earlier non-DiSEqC units (one-band LNBs)
– dc current of 13-V/18-V (for switching horizontal/vertical (H/V)
polarization)
• Earlier non-DiSEqC units (two-band LNBs)
– dc current of 13-V/18-V (for switching between H/V polarizations)
– Continuous 22-kHz tone signal for low or high band selection
• Non-DiSEqC messages
– dc current of 13-V/18-V (for switching between H/V polarizations)
– Continuous 22-kHz tone signal for low or high band selection
– Tone burst signalling to switch between A and B positions of
two-band LNBs
• Any combination of these signals and DiSEqC messages
It is possible to have DiSEqC and non-DiSEqC signalling on the bus. Having
both types of signals on the bus allows the user to control accessories of both
types and does not require the user to configure the master tuner-receiver/IRD
to a particular command protocol. This is possible because the control data of
both protocols should be the same, and a DiSEqC slave (MC68HC908QT/QY)
will recognize and perform control signals from both command protocols.
Freescale Semiconductor, I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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