I am designing a PCB which connects to a Spartan-6 via a connector (Opal Kelly XEM board). The PCB hosts some analog components which will communicate with the FPGA (ADCs, DACs). The FPGA board itself is completely autonomous (has own clock, PLL, ...).
My input signals to the FPGA are:
- SPI signals (MISO/MOSI/SCK) from different ICs
- LVDS data from the ADCs (serial data) + skew matched clock to latch these data at the FPGA
- CMOS clock signal which may be used to clock the FPGA itself or synchronize certain signals on the FPGA (maybe not used but just in case).
Currently I connected all these inputs to the FPGA data pins (e.g. L32P_0, L2N_0 and L3N_0/L3P_0, L66P_0, L66N_0 etc.)
Now I am wondering if I should connect some or all of these signals to the global clock network (GCLK), e.g. L34P_GCLK19_0, L34N_GCLK18_0, etc).
- Is it a good idea to connect any input that is/can be a clock (will be used in
always @(posedge)to GCLK?
- How would I decide which signals I connect to the data pins vs. GCLK?
- What is the purpose of the global clock network (GCLK pins) and what are the advantages/disadvantages?
- Can the GCLK pins also be safely used as LVDS input (e.g.