Figure 1044.Oscan Scan Packet Content/Tapc State Relationships - STMicroelectronics SPC572L series Reference Manual

RM0400
and included in shift TAPC states in certain OScan formats. The modulation of Scan Packet
content with TAPC state varies by scan format.
TAP
Controller
State
C
Advanced
Protocol
Packets
Legend:
OScan scan formats replicate four functions in two forms:
•
OScan0 – OScan3: Providing the best performance for a test clock source by the
target system.
•
OScan 4 – OScan7: Providing the best performance for a test clock sourced by the
external tool.
The OScan4 – OScan7 scan formats are more efficient, as EOT escape sequences are
used to identify an exit from the Shift-xR TAPC state. A Scan Packet associated with the
Shift-xR TAPC state does not include a TMS bit. Instead, and EOT escape sequence
overlaid on an nTDI bit causes an exit from shift TAPC state with no exit from this state
occurring otherwise. A look at the 32-bit DR-Scan shows the impact of this optimization. A
total of 96 bits are required when each Scan Packet associated with a Shift TAPC state
when TMS is included in these Scan Packets while a total of 64 bits are required when TMS
is not included in these Scan Packets. Assuming the EOT escape adds the equivalent of
three bit periods, the number of TCK periods fo this transfer is 67/96 or roughly 70% of the
total without this optimization.
These scan formats may only be used with an external tool sourced TCKC as EOTs are
utilized to improve its performance. The OScan0 – OScan3 Scan Formats always have a
TMS bit included in the Scan Packet. The OScan scan format use case summary is shown
in Table 996.
IEEE 1149.7 Compact JTAG Test Access Port Controller (CJTAG)
Figure 1044. OScan Scan Packet content/TAPC state relationships
SP SP SP SP SP
SP = Scan packet including at least TDI data
SP = Scan packet including at least TMS control information
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SP SP SP SP SP SP SP SP SP SP SP
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