Well, for the past two days I've been using the oscilloscope in analog mode...
which limited me to 4 channels, I couldn't look at both chip selects at the
same time. And, I think that was the biggest problem of all, when you're trying
to toggle one but not the other, I was either confusing myself and not
bothering to run the executable twice, switching things out, or I don't know
Our resident EE seems to always be out, but helped me get the digital channels
I'm looking at 6 channels, ADBUS0-4 and ADBUS7 (as a control).
They are in the picture as follows:
0 - SCK - ADBUS0
1 - MOSI - ADBUS1
2 - MISO - ADBUS2
3 - CS - ADBUS3 (NSS_CONFIG in the Semtech data sheet)
4 - ADBUS4 (also chip select, NSS_DATA in the Semtech data
5 - ADBUS7
If both ADBUS3 and 4 are low, it's as if I selected ADBUS3. I've had some
decent luck moving data both in and out for that (NSS_CONFIG, the radio's
config registers, a few read-onlys).
I've yet to have any luck with reading from NSS_DATA (the radio's fifo where it
stores incoming packets, or where you write to to send out packets). But I
think this gives a clearer picture.
http://imgur.com/6rsEb.jpg (My apologies for the image quality... I have a
crappy camera phone.)
As you can see, ADBUS4 goes low, the clock starts wiggling... MOSI and MISO are
both low. ADBUS3/CS is high... so my chip selects are where I want them to be.
On page 38 of http://www.semtech.com/images/datasheet/sx1211.pdf It says that
it's compulsory to toggle NSS_DATA (ADBUS4) high between each byte read. No
commands need be put on MOSI, if you start toggling the clock with ADBUS4 low
(and ADBUS3 high), MISO should start spitting out data.
Now, it could *possibly* be that there's no data to read... but on the serial
port version of this radio, I'm seeing a packet coming in about every second
here in the office. And since I keep trying to read one byte at a time, for as
long as several minutes, I should get *something*. All zeros, the whole way.
Another possibility is that the radio's not in receive mode, but this seems
even less likely than that there are no packets in the fifo.
Now, if I don't toggle NSS_DATA/ADBUS4 high, I shouldn't expect to keep getting
bytes. But I should get something the first time around. And I'm not.
The other thing is, in the data sheet it says "To read bytes from the FIFO
the timing diagram below should be carefully followed by the uC." So, maybe
I'm not doing it as perfect as I should be, my code is still rather sloppy.
To look at their diagram, the clock starts up no more than 1 cycle after
ADBUS4 goes low. But on the scope, I'm seeing at least 3 or 4 cycles worth. Is
that the problem? And how do I tell this dumb thing to toggle high again more
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