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 CPU selection. Test Access Port (TAP) scan frequency is usually bound to target CPU system clock and it is couple of times slower.

 

When JTAG chain contains multiple TAPs the Instruction Register (IR) and (Data Register) DR prefixes and postfixes must be properly configured:

•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

 

winIDEA can help detect the connected TAPs. Please refer to information about Hardware Tools JTAG chain dialog. There winIDEA reports detected IR offsets of detected TAPs which are same as IR Prefixes or offset from TDO of last* TAP.

* 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

Note that the TDI from the JTAG Connector should be connected to the TDI of the first device in chain; and the TDO from the last device in chain should be connected to the TDO on the JTAG Connector.