User's Manual

RVP8 User’s Manual
October 2005
TTY Nonvolatile Setups
3–28
AFC span– [–100%,+100%] maps into [ –32768 , 32767 ]
AFC format– 0:Bin, 1:BCD, 2:8B4D: 0, ActLow: NO
AFC uplink protocol– 0:Off, 1:Normal, 2:PinMap : 1
The RVP8’s implementation of AFC has been generalized so that there is no
difference between configuring an analog loop and a digital loop. The AFC feedback
loop parameters are setup the same way in each case; the only difference being the
model for how the AFC information is made available to the outside world. Many
types of interfaces and protocols thus become possible according to how these three
questions are answered. AFC output follows these three steps:
S The internal feedback loop uses a conceptual [–100%,+100%] range of values.
However, this range may be mapped into an arbitrary numeric span for eventual
output. For example, choosing the span from –32768 to +32767 would result in
16-bit AFC, and 0 to 999 might be appropriate for 3-digit BCD; but any other
span could also be selected from the full 32-bit integer range.
S Next, an encoding format is chosen for the specified numeric span. The result of
the encoding step is another 32-bit pattern which represents the above numeric
value. SIGMET will make an effort to include in the list of supported formats all
custom encodings that our customers encounter from their vendors.
S Available formats include straight binary, BCD, and mixed-radix formats that
might be required by a specialized piece of equipment. The “8B4D” format
encodes the low four decimal digits as four BCD digits, and the remaining upper
bits in binary. For example, 659999 base-10 would encode into 0x00419999
Hex.
S Finally, an output protocol is selected for the bit pattern that was produced by
encoding the numeric value. The bits may be written to the eight RVP8
backpanel RS232 outputs, or sent on the uplink as a value to be received by the
RVP8/IFD and converted to an analog voltage. Yet another option is for the bits
to be sent on the uplink and received by the DAFC, which supports arbitrary
remapping of its output pins.
To summarize: the internal AFC feedback level is first mapped into an arbitrary
numeric span, then encoded using a choice of formats, and finally mapped into an
arbitrary set of pins for digital output. We are hopeful that this degree of flexibility
will allow easy hookup to virtually any STALO synthesizer that one might encounter.