Table 30 AFC Output Process for Internal AFC Feedback
Step Description
1. Map AFC feedback level to
an arbitrary numeric span.
The internal feedback loop uses a conceptual [-100%,+100%] range of
values.
This range may be mapped to an arbitrary numeric span for eventual output.
Any span can be selected from the full 32–bit integer range.
For example, choosing the span from -32768 ... +32767 results in 16–bit AFC,
and 0 ... 999 might be appropriate for 3–digit BCD.
2. Encode AFC feedback level
using a choice of formats.
An encoding format is chosen for the specified numeric span to produce
another 32–bit pattern which represents the above numeric value.
Vaisala supports formats for most custom encodings that our customers
encounter from their vendors. Available formats include straight binary, BCD,
and mixed–radix formats that might be required by specialized 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 encodes to
0x00419999 Hex.
3. Map AFC feedback level to
an arbitrary set of pins for
digital output.
An output protocol is selected for the bit pattern that was produced by
encoding the numeric value.
The bits may be sent to the IFDR and converted to an analog voltage, or they
may be retransmitted by the IFDR as a serial stream to be received by an
outboard DAFC module (which supports arbitrary remapping of its output
pins).
Pinmap Uplink Protocol Parameters
These parameters are available when you select the PinMap uplink protocol.
The table assigns a bit from the encoded numeric word to each of the 25 pins of the
RVP900/DAFC module. For example, the default table assigns the low 25 bits of the
encoded bit pattern to pins 1 ... 25 in that order. You can also pull a pin high or low by
assigning it to +5 or GND. Such assignments produce a logic–high or logic–low signal level,
not a power or ground connection. The latter must be done with physical wires.
One RVP900/DAFC pin can optionally be selected as a Fault Status indicator. You may
choose which pin to use for this purpose, as well as the polarity of the incoming signal level.
The standard RVP900/DAFC module only supports the selection of pins 1, 3, 4, 13, 14, and 25
as inputs. This setup parameter allows you to choose any pin, however, because it does not
know what hardware may be listening on the uplink and what its constraints might be.
PinMap Table (Type ’31’ for GND, ’30’ for +5)
------------------------------------------------------
Pin01:00 Pin02:01 Pin03:02 Pin04:03 Pin05:04
Pin06:05 Pin07:06 Pin08:07 Pin09:08 Pin10:09
Pin11:10 Pin12:11 Pin13:12 Pin14:13 Pin15:14
Pin16:15 Pin17:16 Pin18:17 Pin19:18 Pin20:19
Pin21:20 Pin22:21 Pin23:22 Pin24:23 Pin25:24
FAULT status pin (0:None): 0, ActLow: NO
RVP900 User Guide M211322EN-J
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