PCB Fiducial Markings
This week I tried solving the problem I was facing with putting the FPGA in configuration mode, which I have also explained in my blog last week. The main issue is that after TCPIP_STACK from Harmony Configurator is initialised, pin D0 will not be configurable anymore. I have tried reading the peripheral selection register for pin D0 (RPD0R), it reads 0000. According to the data sheet, 0000 corresponds to “No Connect”, which means the pin is used as a normal I/O. However, I am still unable to write or read the pin, if TCPIP_STACK is initialised.
I also had to add fiducial markings to the PCB design based on the manufacturer request. I found a very good Reference on the size, number and placement of fiducial marks. In a nutshell, diameter of the fiducial should be between 1mm – 3mm with a clearance of 3R, where R is the radius. The size of different fiducial markings in a board should not vary. They should be placed a triangular form as far from each other as possible.
I am currently trying to include HOTP (HMAC-based one-time password) in my code to increase the security of the connection. It is based on the code done by one of the previous interns. I’m still trying to solve the problem with TCPIP_STACK…