ITP700 Debug Port Design Guide

R
ITP700 Debug Port Design Guide 77
10 Appendix A – Alternate Bypass
Methods
Sections 1.5.2 and 2.5.2 of the attached document describes the recommended bypass method for
the ITP scan chain using a four-pin header. The four-pin header is preferred due to the
characteristic it has of completely removing the TDO pin from the TDI/TDO path to the next scan
chain agent. There are other methods possible for completely bypassing populated scan chain
agents. Figure 21 describes a method of completely bypassing the last agent of a scan chain using a
three-pin header. Note that this method would require 75 Ω pull ups to VTAP on the TDO pins of
both P0 and P1. Figure 22 illustrates a method of completely bypassing two agents using a three-
pin header and a pair of two-pin headers.
Figure 21. Complete Bypass of One Out of Two Agents
P0
TDI
TD0
TDI
TD0
P1
TDI TD0
1
2
3
P0 or P0,P1
Figure 22. Complete Bypass of Two Agents with Three Headers
P0
TDI
TD0
TDI
TD0
P1
TDI TD0
P0 or P1 or P0,P1
1
2
3
JP1
JP3
JP2
P0
P1
P0,P1
OUT
IN
OUT
2,3
OUT
1,2
OUT
IN
IN
JP1 JP2 JP3
Debug Port