Reconnecting to a Target Device with a Lower JTAG Clock Frequency - 2021.2 English

Vivado Design Suite User Guide: Programming and Debugging

Document ID
UG908
Release Date
2021-10-22
Version
2021.2 English

The JTAG chain is as fast as the slowest device in the chain. Therefore, to lower the JTAG clock frequency, connect to a target device whose JTAG clock frequency is less than the default JTAG clock frequency.

You should attempt to open with a default JTAG clock frequency that is 15 MHz for the Digilent cable connection and 6 MHz for the USB cable connection. If it is not possible to connect at these speeds, Xilinx recommends that you lower the default JTAG clock frequency even further as described below.

To change the JTAG clock frequency, use the Open New Hardware Target wizard, from Vivado® Design Suite, as shown in the following figure.

Figure 1. Vivado Lower JTAG Frequency

Alternately, you can use the following sequence of Tcl commands:

open_hw_manager 
connect_hw_server -url machinename:3121
current_hw_target [get_hw_targets */xilinx_tcf/Digilent/210203327962A] 
set_property PARAM.FREQUENCY 250000 [get_hw_targets */xilinx_tcf/Digilent/210203327962A] 
open_hw_target