[hpsdr] What is the best way to interface Hermes to a non standard filter/PA/Transverter network?

[Rob Frohne]

Hi All,

I've decided to hook my Hermes to the guts of an old FT-847 (that was 
hit by lightning, wiping out most of the 5 volt logic) for the bandpass 
filters, the PA units with their LP harmonic filters and the the 
transverter units for 2 meters and 440 MHz.  The FT-847 uses a clocked 
data input similar to the SPI or I2C that are available on the Hermes 
board for Alex & Apollo, and shift registers similar to Apollo and Alex, 
but the bits are defined differently to tell the the units what band you 
are using, etc.  I'm mulling over the best way to fix this little 
problem so that my maintenance headaches are as minimal as possible.  
Here are some options I have considered.

1)  Change the FPGA logic so that I get what I need on the Apollo/Alex 
connectors.  (They are really wired in parallel, with perhaps a 
different pin-out on the Hermes board.)  This means I need to apply the 
patch every time Phil or someone else updates the Hermes firmware.

2)  Use a couple of the pins that are GPIO on J16 to make my serial 
interface with clock and data.  This may also mean that I have to apply 
a patch every time, but maybe not if I can convince everyone that those 
GPIO pins are just as well used for this purpose.

3)  Use two of the three lines on J14 (labeled for future expansion) for 
my serial interface.

4)  Do the mapping in the software.  I don't think this is a good 
option, because software changes much more rapidly than hardware, and 
the mapping probably is not always an easy thing, because Hermes has 
options for different antennas, low and high pass cutoffs, etc. whereas 
I need just which of the ten HF frequency bands for receive (in order) 
and then low, medium or high HF transmit, or VHF transmit, or UHF 
transmit, and then data regarding the attenuator and preamplifier.  See 
the block diagram image 
<http://people.wallawalla.edu/%7ERob.Frohne/FT-847/Filter_Interface.png> 
of the FT-847 setup below, or the complete block diagram 
<http://people.wallawalla.edu/%7ERob.Frohne/FT-847/FT-847%20Block%20Diagram.pdf>.

Is there something I haven't thought of that is better?  I'm leaning 
toward 3) the future expansion pins, but would like some advice from 
those who have more experience than I do.  Suggestions?

Thanks & 73,

Rob
KL7NA


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