[hpsdr] [OZY] Initial OZY Schematic Posted For Review and Comments - May 10, 2006

[Lyle Johnson]

Hello Phil!

> Please review and make comments.
> 
> Some initial questions:
> 
> 1.  Do we need external SRAM?  There are 26 RAM blocks of 4608 bits
> (including parity) each in the Cyclone II EP2C5Q208C8 part that I am
> using.  I can probably fit in a 128Kx8 (1Mb) SRAM but, if populated,
> it will use up the 32 expansion IO lines that are left from the FPGA.

I think no.  The FX2 is there primarily to act as a USB interface. 
Extra memory might be good for buffering, but then the host computer 
probably has lots of memory for that purpose.

If we need a CPU in the HPSDR box with a lot of memory, we may want to 
just make a board that provides that, along with the IO we might want 
for local control, CAN bus, etc.  Perhaps an ARM or something similar.

> 2. Are 8 optional SMT LEDs tied to the FPGA_GPIO[1-8] lines enough for
> status/debugging use?  These would not be of much use if I add the
> SRAM to those lines, so that is why I call them optional.

Should be enough.

***

I note that the async port lines come to a 4-pin header.  If there s 
room, I'd like to see these buffered to RS232 levels even if we can't 
fit a DE9 connector or pair of DE9 connectors to the board.  Almost 
anyone who uses these lines is going to have to buffer them, so we might 
as well do it.  We won't have charge pump noise since we have +/-12 
available.  An SN75C1406 is small, has enough lines,and is cheap.  If we 
lack space for a DE9, we could put in a 2x5 header that, with a 
pin-for-pin ribbon cable would result in the correct pin out for a DE9.

Also, I wonder if the reset line should go to an ATLAS pin?  If we have 
several processor eventually installed, it might be good if they can 
come out of reset at roughly the same moment so we don;t have to write 
all sorts of code to get things sync'ed up.  A reset voltage monitor 
chip could eliminate threshold ambiguity, such as an MCP120 series part 
from Microchip.

Finally, is it worth adding a physical reset button so we can bump it 
and wonder why the FX2 rebooted?

73,

Lyle KK7P


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