I'm working with a board design that uses a Xilinx CoolRunner II CPLD (XC2C256-7VQ100I). We're currently working with the customer, and setting up the pins they'll be using external from our board to control our device. JTAG has several lines we'll use to program the CPLD on each part (TDO, TCK, TMS, TDI). In our production environment, we'd like to use several external pins to hook up to these lines to program the device. However, the end customer would like to ground these pins (Since our product will be fitting into an existing design). My question is, will there be any repercussions I need to consider about grounding those 4 pins on the device? (On the CPLD the JTAG lines are pins 45, 47, 48, 83). I'm fairly sure it shouldn't cause any issues, but haven't yet been able to find a definitive answer.
Grounding the JTAG input lines (TCK, TMS, and TDI) is fine, although it'll make the port unusable. The JTAG output, TDO, is another matter — grounding it will cause a short circuit if it is driven high by the CPLD! If you cannot bring JTAG out to a dedicated set of pins, you're probably best off leaving it disconnected.
If unsure, you can simply add a series resistor to limit any shortage currents.
Of course, this would lead to power loss in case those JTAG pins are driven HIGH. But at least it won't blow anything up.