winIDEA Help

This chapter explains JTAG clock and JTAG chain settings. Open Hardware / CPU Options / JTAG.

 

 

 

Scan speed

Scan speed depends on the CPU clock and Target board PCB design.

 

 

Number of idle TCKs

Define number of trailing TCK cycles after JTAG scan returns to Test-Logic-Idle JTAG state. Can be used to increase communication robustness at higher JTAG speeds.

 

Use Scan speed during Initialization

This option is useful on systems which start very slow. Slower scan speed can be used for first initialization sequence (see Initialization Sequence details), during which the CPU clock is raised (PLL engaged) and then higher scan speeds can be used for download and later while debugging.

 

Do not use TRST line - Enable this when assertion of JTAG TRST line is not desired. TAP will be reset only by clocking through Test-Logic-Reset JTAG state.

 

JTAG chain

Enable option This is the single device in the JTAG chain when only target CPU is connected to debug connector. Multiple TAPs inside target SoC are handled by winIDEA accordingly to the CPU selection. The scan frequency of the Test Access Port (TAP) is typically synchronized with the target CPU's system clock and is generally a few times slower.

 

When the JTAG chain contains multiple TAPs, the configuration of the Instruction Register (IR) and Data Register (DR) prefixes and postfixes is crucial:

•IR Prefix to the sum of IR lengths of all following* TAPs

•IR Postfix to the sum of IR lengths of all preceding* TAPs

•DR Prefix to the number of following* TAPs

•DR Postfix to the number of preceding* TAPs

 

* In a topology sense in direction from Test Data Input (TDI) to Test Data Output (TDO). Pre/post terminology was chosen based on when filling bits need be shifted into TDI.

 

 

Example of the JTAG chain