Hallo,
aus einem Lattice-Dokument.
http://www.latticesemi.com/lit/docs/ispbs/ispguide.pdf?jsessionid=f0306f5fc75d9df7248c417135155c3a561f
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Pin Connections After Programming
After programming and testing has been completed, the question often
arises, “What should be done with the ISP
port signals?” One of the requirements in the IEEE1149.1 standard for
the JTAG port is that both the TMS pin and
the TDI pin have internal pull-up resistors. By ensuring that there is a
‘1’ on the TMS pin, inadvertent clocking of
TCK will not cause the JTAG state machine to leave its reset state.
During power-up, inadvertent clocking on TCK
can cause the 1149.1 state machine and instruction register to come up
in an undesirable state. To increase noise
immunity during power-up, the following recommendation is made:
• A 4.7KΩ pull-up resistor should be used on the TMS signal and a 4.7KΩ
pull-down resistor on the TCK signal on a board. As the number of
devices connected to the TCK/TMS signals increases, the pull-up and
pull-down resistor values may need to be adjusted as more internal
pull-up resistors are affecting those signals.
For a chain with 10 devices, the pull-down resistor value on TCK should
be 2KΩ.
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