HSMC loopback adapter makes JTAG unusable

[Altera_Forum]

Hello, 

 I am trying to use an HSMC loopback adapter on my Cyclone V SoC dev kit to debug it with SignalTap over the integrated USB Blaster. Each time I connect the HSMC loopback adapter, I cannot scan the JTAG chain any more.  What can I do to solve this issue (apart from removing the loopback connector...)?  Thanks in advance.  Edit: I have just found out that die HSMC connector is also connected to the JTAG. Is this disableble ( nice word :D) ?

[Altera_Forum]

A problem about reading the user manual! Find out what SW4 - JTAG ENABLE is made for.

[Altera_Forum]

Weeellll... I actually forgot to mention that: I already tried both possibilities: 

 - HSMC is bypassed: I cannot even connect to the JTAG chain - HSMC is enabled: I cannot see the devices on the JTAG chain, but cannot successfully program the FPGA.  Edit: I switched over to another Board, which worked out the box with the same configuration. So the reason was a faulty device.

[Altera_Forum]

The switch must be in "bypass" position when nothing is connected to HSMC.  

 I also see that the HSMC JTAG lines are not isolated by the multiplexer.  So the problem might be that the loopback adapter is shorting a JTAG line. Or it does not short it but the capacitive load compromises the signal integrity. There should be no problems with the original loopback adapeter. It connects TDI to TDO, JTAG should even work in HSMC bypass or enable position.

[Altera_Forum]

Thank you for your reply, but as I edited into my last post, my device was defective.

[Altera_Forum]

I am still trying to find out WHY my board does not work.  

 Is it normal that the voltage of the JTAG-TDO of the HPS is 3,3V as this exceeds the maximum absolute ratings specified for the analog switches used to configure the JTAG chain (absolute maximum voltage: Vcc + 0,5V)?