Untwisting RPi5 Camera Connectivity
~ How to connect FPGA to 4-lane MIPI camera w/o shorts and smokes ~
Objective:
Attach Sony IMX283 20MP “OneInchCamera” chip to
Trenz TEB0707-02 Carrier Card with TE0711-01 FPGA SOM
Background info:
The camera connectors found on most of the previous models of Raspberry Pi were FFC (or even FPC) 15pin@1mm (15mm total, PN=SFW15R-2STE1LF) for up to 2-lane CSI imagers. Also known as “Standard” MIPI connector, this end-to-end-system was designed for the OPPOSITE CONTACT CABLE, such as illustrated below.
1) ”Standard” 15pin@1mm CSI connectivity. Note cable reversal.
Correct use:
Incorrect use:
Starting with RPi5, this has changed to 22pin@0.5mm (11mm total, PN=54548-2271) for up to 4-lane HD cameras. Also known as “Mini” connector, this end-to-end system was designed for the SAME CONTACT CABLE. Part of the reason for making this change was to reduce the chance of misconnects shown in the second illustration of “Standard” system.
2) Hybrid system, with 22pin@0.5mm “Mini” on one end, and 15pin@1mm “Standard” on the other
22-pin / 0.5mm "Mini"
15-pin /1mm "Standard"
Contacts are now on the same side of cable. The cable also adapts the width and pin pitch. Despite featuring more pins, which are now denser, the new “Mini” connection is on the narrower side of the adapter cable.
3) Complete “Mini” system. Contacts are on the same side of the cable, exactly like on the Hybrid system (*)
However, we have seen designs that assume the use of “Opposite Contacts” “Mini” cable. While such cables exist and can be purchased separate from the camera, they are not a norm. Indeed, the cable that comes with 4-lane IMX283 camera does not have “Opposite Contacts”.
- The use of incorrect cable results in a direct short of the 3.3V camera supply.
It is exactly our repeated seeing of improper connection, at times even resulting in smokes, which prompted this article. We show on the next page the proper way to go about it.
Connector Pinout towards 4-lane Camera:
There is a very simple rule to apply here: The MIPI connector going into FPGA should be pinned exactly like the RPi5.
The RPi5 pin assignment for MIPI connector is shown in Table1 below. The corresponding connector on the camera side is also illustrated.
Note the pinout inversion from Camera to RPi5 (or FPGA) Board. This comes from the combination of:
(1) 180-degree rotated connectors and
(2) “Same Contact” cable.
This connector rotation on the “Standard” system is compensated by the “Opposite Contact” cable. The “Mini” system however, by using the “Same Contact” cable, counts on the RPi5 board for this compensation.
Conclusion:
While this may seem like a no-brainer, the real-life experience is proving that the designers may take it for granted and, without putting any thought into end-to-end system connectivity, mechanically pin-for-pin match the FPGA-side connector with Camera connector.
That works, as long as the “Opposite-Contacts” flat cable is used.
But then, when they plug camera into their FPGA card using stock cable that came with it, the whole system crashes, and may even start smoking. While replacing the cable would fix this problem, the proper long-term solution is to reverse the connectivity on FPGA board, to so prevent your customers from repeatedly shorting the 3.3V supply when they do the first natural thing, which is to connect their camera with its stock cable.
We hope this little tidbit from our empirical toolbox helps you keep happy at designing apps and boards for FPGA :).
(*) Not to be mistaken, this discussion is for the serial MIPI CSI type of interfaces. There are also non-MIPI camera interfaces. One of the most popular is DVP24, which is a 24-pin parallel interface, with 0.5mm pin pitch. DVP stands for Digital Video Port. The DVP is not subject to Mobile Industry Processor Interface (MIPI) licensing limitations. Being parallel, the DVP is much simpler to work with, but cannot match the MIPI data throughput. DVP is therefore not suitable for imagers with high resolution and high frame rates.
