ARM Technical Support Knowledge Articles

In which direction do the debug scan chains scan?

Applies to: ARM920/922T, ARM940T, ARM9TDMI

Answer

ARM9TDMI-based cores are provided with debug scan chains 0, 1 and 2.

The Technical Reference Manual (TRM)  for each core specifies which bits are included in each scan chain, but does not state explicitly which end of each chain is the input (TDI) and which end is the output (TDO).

The scan chain orders are:

Scan Chain

TDI

TDO

 0

ID[0]

 INSTREXEC

 1

ID[0]

 DD[0]

 2

 Read/Write

Date value [0] 

The full scan chain bit order may be found in each TRM as follows:

 CoreTRM Chain 0, 1 Chain 2
 ARM9TDMIARM DDI 0145B pp 6-3 to 6-5 p 5-25
 ARM920TARM DDI 0151C pp 9-24 to 9-28 p 9-29
 ARM922TARM DDI 0184B pp 9-24 to 9-28 p 9-29
 ARM940TARM DDI 0144B pp 10-4 to 10-6 p 8-22

Article last edited on: 2008-09-09 15:47:44

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