In which direction do the debug scan chains scan?

Applies to: ARM920/922T, ARM940T, ARM9TDMI

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:

Core	TRM	Chain 0, 1	Chain 2
ARM9TDMI	ARM DDI 0145B	pp 6-3 to 6-5	p 5-25
ARM920T	ARM DDI 0151C	pp 9-24 to 9-28	p 9-29
ARM922T	ARM DDI 0184B	pp 9-24 to 9-28	p 9-29
ARM940T	ARM 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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