[amsat-bb] RAFT and ANDE telemetry?

Robert Bruninga bruninga at usna.edu
Fri Dec 22 08:08:04 PST 2006

> could you explain the 8 status bits, please?
> And the meaning of the last 3 digits? 
> T#529,083,002,036,035,071,10000000,000
>                           ^^^^^^^^ ^^^

This is the standard APRS telemetry frame which can report up to
5 analog inputs, and 8 digital discretes.

In the original 1995 APRS Mic-E MIM module they were a fully
independent 8 bit I/O port.  Useful for discrete status bits.
In the Kantronics 9612+ TNC, they are also a separate 8 bit I/O
port (as used on PCSAT-1 and PCSAT-2) good for both inputs and
commanding.  But on the KPC-3+ TNC, they are mostly the same
port as the analog telemetry pins.  

We find these Kantronics TNC's to be very powerful.  That is why
we now have a total of 8 of them in space oas the primary
command/control system for several satelites, and use another
few dozen in out LAB satellites for the students to learn
elements of satellite comms.

Actually the KPC-3+ has 8 A/D inputs, but only 2 are brought to
the connectors.  We bring out 3 more for a total of 5.  But 3
are used internally and so that is why we only have 5 channels
of telemetry.  The first two bits are used for RS-232
handshaking inputs, DTR and RTS.  On RAFT we actually use the
DTR line (the first "1" above") as the SIGN bit for the battery
current sensor.  If it is 1, then the current into the battery
is negative.  In this case, 002 shows no input current from the
sun, so the 036 current is out of the battery.

On ANDE, we use both the DTR and RTS pins as a 2 bit counter to
indicate which of the four sets of telemetry are being
transmitted.  We call those the FRAME counter bits.  So here is
the definition of those 8 bits on any KPC-3+ TNC:


Where D and R are the DTS and RTS inputs
I is used internally?
5,3,2,1,0 are the 5 analong inputs which show in the telemetry
frame as T#SSS,000,111,222,333,555

But we have always called them 1,2,3,4,5 in our documents for

So in the 8 discrete bits, the "1"'s and "0"'s besides the first
two and the internal one, are simply a binary reflection of the
same 5 channels  of telemetry as the actual 5 analog inputs.  If
they are above the digital threshold, they show as a "1" and if
below the threshold, they show as a "0".  Since the "I" pin is
used internally (something to do with the optional real-time
clock chip, it is not invovlved in the TELEMETRY command.

However, you can see it's value and might be able to still use
it as a on/off discrete indicator I guess.

Anyway, with the inputs, and outputs, and password protected
logon built into every TNC, we find them a powerful tool for all
kinds of applications, not just APRS...

OH!  And the last 3 digits on the end are a memory wash counter.
We are looking for SEU hits on the RAM chip.  All unused RAM is
painted with a bit pattern, and periodically, the TNC checks for
bit errors.  It acumulates a total  until the next reset.  This
was custom code we asked Kantronices to add for this mission to
give us some "science" data.  But there was never enough time to
test it completely and we noticed on the ground that it would
often jump to 999 on its  own even on boot up.  So we will
probably ignore it...


> > Here is the RAFT tlm. I heard some packet signals but I 
> > only decoded one packet.
> > 
> > RAFT>BEACON,SGATE [21-Dec-06  14:49:40] <UI>:
> > T#529,083,002,036,035,071,10000000,000
> This is GOOD NEWS!
> It shows that RAFT is now charged up enough to make it through
> eclipse.  Notice that the telemetry serial number is up to
> which means it has now been running for 529 minutes since it
> last booted up.  This is good news, because on the first few
> orbits, it was going to low-power shutdown towards the end of
> eclipse.
> Thanks!
> Bob, WB4APR
> USNA Satellite Lab
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