Question about custom BOB for a 7i92

PCW, any thoughts on adding an external SPI connector on the same channel as the 4 onboard devices?

Not sure if this is a great idea but I started reworking the PCB with the multiplexer and decoder you suggested and since I have a bunch of extra CS lines and a spare pin for MOSI.....

The thought is to use a buffer IC like a CD74HC126 on the external connector as I'm sure the drive strength would be an issue. I have no actual use for this ATM, just "might as well"

Yes, you could add an external SPI port
Note that if you buffer MISO you need to
enable the buffer with the chip select
(and that buffering will slow things down a bit)

PCW wrote:

Yes, you could add an external SPI port
Note that if you buffer MISO you need to
enable the buffer with the chip select
(and that buffering will slow things down a bit)
 

I was planning on using an on-board jumper to enable all buffers as well as the buffering the external CS (maybe not necessary with the decoder output), so basically the connector is dead unless the jumper is on and presumably not being instantiated via the component.....or is there some issue with the MISO buffer being on when the external chip is not selected via CS?

Also thinking of multiplexing the outputs so I can squeeze 2 more stepgens in there for rev2. I only see "OutM" in the hostmot2 docs, I assume that's an output mux that I can use a multiplexer with 3 address lines and a direction line with like inMux? Can the FPGA handle 8 stepgens along with the rest of what I stuffed in there?.

That first pinout still relates to the PCB I have on the way so that's the actual firmware I need for now (with the frame pin on CS_A1 as you suggested).

There is no muxed output module currently So I would not count on that

(If i do this eventually I would use a shift register like the 74HCT595)

Have to figure out whether I want to ditch SS or not then, starting to ask alot of that little board.

I'm not terribly familiar with decoders, multiplexers or SPI in general but this is what I'm looking at.
 

Edit, Edit,
Had to look at it about three times to understand the issue. I suppose the issue is the buffer overcoming the MISO line cancelling out the other devices on the line?

BTW, appreciate the help.....didn't expect it to get this complicated.

Maybe something like this