Chapter 3 _______________________________________________________ Hardware Installation
VAISALA_______________________________________________________________________ 93
3.5 IFDR DAFC Uplink Protocol
This section describes the interface from the IFDR to the DAFC. The
interface is actually backward compatible to the legacy RVP7. These
hookups are less conventional than the "standard" interfaces described
earlier in this chapter, but they sometimes can supply exactly what is
needed in exactly the right place
3.5.1 Using the Legacy IFD Coax Uplink
In the previous RVP7 processor, the Coax Uplink was the IFD single line
of communication from the main processor board. All of the information
that was needed by the IFD arrived through this uplink. As such, it
contained information that might also be useful for other parts of the radar
system. In particular, it is a convenient source of DAFC.
The RVP900 uses a single CAT5e Uplink/Downlink cable between the
IFDR and and computer server. The legacy coax uplink protocol is no
longer used directly; but to help with backward compatibility, the
waveform is now synthesized as an output from the IFDR. Any hardware
that used to be attached to the RVP7 coax uplink can still be driven from
this new IFDR port.
The uplink is a single digital transmission line that carries a hybrid serial
protocol. The two logic states, "zero" and "one", are represented by 0 V
and +12 V (open circuit) electrical levels. The output impedance of the
uplink driver is approximately 55Ω . When the cable is terminated in 75Ω,
the overall positive voltage swing is approximately 8.6 V.
The electrical characteristics of the uplink have been optimized for
balanced "groundless" reception. The recommended eavesdropping circuit
is shown in Figure 23 on page 92, and consists of a high-speed comparator
(Maxim MAX913 or equivalent) and input conditioning resistors. Both the
PinMap Table (Type 31 for GND, 30 for +5)
Pin01:GND Pin02:GND Pin03:GND Pin04:GND Pin05:GND
Pin06:GND Pin07:15 Pin08:14 Pin09:13 Pin10:12
Pin11:11 Pin12:10 Pin13:09 Pin14:GND Pin15:GND
Pin16:GND Pin17:08 Pin18:07 Pin19:06 Pin20:05
Pin21:04 Pin22:03 Pin23:02 Pin24:01 Pin25:00
FAULT status pin (0:None): 5, ActLow: YES
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