Altera JTAG监测求教 Altera, JTAG, 监测, 求教

qycct

JTAG调试时发现不能连续监测，跑一会就退出，提示的错误有三种（一次出现一种）：
Error: Can't find the instance.  Download a design with SRAM Object File containing this instance.
Error: Can't continue the established JTAG communication.  Reconnect communications cable and device.
Error: Can't engage JTAG communication.  Select correct communications cable and device.

      请大大们帮我解惑。