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OnCE™ Module

12.10.3 Loading the JTAG Instruction Register

JTAG instructions are loaded in via the IR path in the state machine. Shifting takes place in the Shift-IR path, while the actual instruction register update occurs on Update-IR.

NOTE:

The bit order for JTAG/OnCE shifting is always as shown in Figure 12-17.

TDI

 

 

MSB

OnCE Shifter

...LSB

 

TDO Logic

 

 

 

 

 

 

 

 

 

 

Figure 12-17. Bit Order for JTAG/OnCE Shifting

The following sequence shows how to load the instruction DEBUG_REQUEST into the JTAG IR, as shown in Figure 12-18.

JTAG

State

TCK

TMS

TDI

TDO

 

Test-Logic-Reset

 

Run-Test/Idle

 

Select-DR-Scan

Select-IR-Scan

 

Capture-IR

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

= Don’t Care

Shift-IR

Exit1-IR

Update-IR

 

 

 

 

 

 

OS0

OS1

 

 

 

= Tri-State

Run-Test/Idle

AA0842

Figure 12-18. Loading DEBUG_REQUEST

During Shift-IR, a 4-bit shifter is connected between TDI and TDO. The opcode shifted in is loaded into the JTAG IR on Update-IR. The data shifted out is captured on Capture-IR. TDI, like TMS, is sampled on the rising edge of TCK and changes on the falling edge of TCK. TDI is first sampled on the TCK rising edge, following entry into the Shift-IR state, and is last sampled on the TCK rising edge when entering

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DSP56824 User’s Manual

 

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