On the 2805x device, the JTAG port is reduced to 5 pins (TRST, TCK, TDI, TMS, TDO). TCK, TDI, TMS and TDO pins are also GPIO pins. The TRST signal selects either JTAG or GPIO operating mode for the pins in Figure 6-42. During emulation/debug, the GPIO function of these pins are not available. If the GPIO38/TCK/XCLKIN pin is used to provide an external clock, an alternate clock source should be used to clock the device during emulation/debug because this pin will be needed for the TCK function.
In 2805x devices, the JTAG pins may also be used as GPIO pins. Care should be taken in the board design to ensure that the circuitry connected to these pins do not affect the emulation capabilities of the JTAG pin function. Any circuitry connected to these pins should not prevent the emulator from driving (or being driven by) the JTAG pins for successful debug.