PCAM 5C and Zynq-7000

[Joao Fragoso]

Is it possible to connect PCAM 5C into Zynq-7000 through a XADC pmod (using some adapter)? Is there any tutorial, example and or suggestions how to do that?

[JColvin]

Hi @Joao Fragoso,

We do not have a tutorial for this; the Pmod ports (at least for Digilent made boards) are tied to 3.3V logic so a normal Pmod port would not work for this. There are a couple of threads that discuss the hardware requirements here and here, with the takeaway being that you will need the LVDS capability (which at least the dedicated XADCs on the Digilent boards do not do). So it may be possible, but not likely and not straightforward to do.

Thanks,
JColvin

[Joao Fragoso]

Hi @JColvin.

Thanks for your replay. I was looking into Zybo schematics and Zybo XADC are routed as differential pair (as High Speeds PMODs) and XADC goes into FPGA bank 35 (as MIPI connection in Zybo Z7). Even I do not use XADC for MIPI connection, since I can not meet all electrical requirements, I do not understand yet why cannot I use XADC in some LVDS interface (including LVDS_25) ? When you mention that PMODs in Zybo are tied to 3.3V, I did not see any difference in Zybo Z7 schematic that make me figure out these differences and why can not use LVDS_25 in Zybo. Where is the difference in these boards for bank 35 (besides MIPI connection)? 

[JColvin]

Hi @Joao Fragoso,

I apologize for the confusion. The XADC pins are on bank 35 like the MIPI pins, but as per the Xilinx user guide for the XADC; they are only able to handle an input range of 0V to 1V (or -0.5 to 0.5V if you are in bipolar mode), so they are not able to handle the 2.5V LVDS logic. Additionally, to use the MIPI CSI-2 interface, the D-PHY physical layer is needed (as detailed in the Pcam reference manual and the XAPP894 from Xilinx). Since the Zynq 7020 chip (presuming you are looking at the Digilent made Zybo Z7-20) does not natively support the physical layer, though Ultrascale chips do support it natively. Because of this, the circuitry needed to be externally added in both the Pcam add-on board and on the Zybo Z7 itself (shown in more detail on page 2 of the Zybo Z7 schematic).

Let me know if you have any questions about this.

Thanks,
JColvin

[Joao Fragoso]

when you say D-PHY physical layer do you mean resistor R46 to R56 in page 2 of Zybo Z7 Schematic (https://reference.digilentinc.com/_media/reference/programmable-logic/zybo-z7/zybo_z7_sch-public.pdf) ?

[JColvin]

Hi @elodg,

I know you're a lot more familiar with the physical and electrical aspects of the MIPI CSI-2 interface; could you clarify with more accuracy than I can provide about the physical layer?

Thanks,
JColvin

[elodg]

On 10/14/2019 at 11:09 PM, Joao Fragoso said:

Is it possible to connect PCAM 5C into Zynq-7000 through a XADC pmod (using some adapter)? Is there any tutorial, example and or suggestions how to do that?

We do not recommend wiring the Pcam 5C to Pmod connectors of any kind. There is the mechanical issue of converting from the FFC connector to the Pmod, the electrical issue of terminating and adapting the D-PHY signals to LVCMOS and LVDS in a 3.3V bank and the issue of transmission losses of Pmod traces. Out of all the great things we could be working on this is the least desired.