STMicroelectronics SPC572L series Reference Manual page 1779

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state progression. The EPU is unaware of the APU's existence. All T4 features are
managed outside of the EPU.
The TAP.7 serialization schemes are specified with scan formats that complement the
JScan 0-3 Scan Formats inherited from the T3 TAP.7. The scan formats are called
advanced scan formats as they support two-signal operation.
Three groups of scan formats (MScan, OScan0-7, and SScan0-3) provide a number of
options for the serialization of scan information for use in a Star-2 scan topology. The OScan
and SScan Scan Formats are broken into two groups with the same function, one group has
better performance but may only be used with an external tool sourced TCKC. The external
tool chooses a scan format that matches the constraints imposed by the application, chip
components, and possibly the external tool itself.
The MScan and OScan formats address Test and Debug use cases. The mandatory MScan
and OScan0-1 formats emphasize flexibility over performance. The remaining optional
Oscan2-7 formats emphasize performance over flexibility by not transmitting unneeded
information such as TDI and TDO in non-shift TAPC state machine states.
The optional capabilities added with T4 and above TAP.7s change the bit sequences seen
at the TAP.7 signals. A TAP.7 controller comprehends only the bit sequences generated by
the use of the features it supports. It is never exposed to bit sequences it does not
comprehend. A check for supporting an enabled feature is made before the feature is used
(alters the bit sequences). When a T4 TAP.7 controller detects the use of an unsupported
scan format, it halts its operation and places itself in a state where its operation may be
resumed. This state is henceforth called "offline". A TAP.7 controller that is not offline is
henceforth called "online". While offline the TAP.7 controller awaits the detection of a special
signaling sequence called the Online Activation Protocol. This protocol sequence places an
offline TAP.7 controller online and synchronizes the operation of all online TAP.7s.
The Advanced Protocol Unit supports the stall of a transfer by both the external tool and
STL at any TAPC state.
The APU provides the following functions:
•
Bypass (for operation with the Standard Protocol)
•
Scan control (for SP use)
•
Configuration Control (for CP use)
IEEE 1149.7 Compact JTAG Test Access Port Controller (CJTAG)
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