Epu Registers - STMicroelectronics SPC572L series Reference Manual

RM0400
60.6.1.5 Exiting a Control Level
A control level is exited when one of the following occurs:
•
The Select-IR-Scan TAP.7 controller state
•
The Test-Logic-Reset state
• Certain TAP.7 controller commands (Exit Control Level – ECL register bit)
•
An event that synchronizes the operation of TAP.7 controllers
60.6.1.6 Zeroing the ZBS Count
Events causing an exit from a control level also zero the ZBS count. Scan Selection
Directives (SSDs) associated with T3 and above TAP.7s zero the ZBS count when the
control level has not been locked.
60.6.1.7 Utilizing ZBSs within the STL
After the Test-Logic-Reset state, ZBSs are used for basic EPU control. ZBSs that are
intended for TAP.7 use are henceforth called "TAP.7 ZBSs". ZBSs that are intended for
other uses are henceforth called "Other ZBSs". Two TAP.7 registers enable the STL's use of
ZBSs. Storing these registers causes a control level exit, zeroes the ZBS count, and
enables the use of Other ZBSs. Storing the Suspend Register (SUSPEND) suspends the
use of control levels. Storing the ZBS Inhibit Register (ZBSINH) inhibits ZBS detection.
When either of these methods is used, the Test-Logic-Reset state enables the use of TAP.7
ZBSs in addition to initializing the TAP.7 controller.
The operation of the TAP.7 controller changes with the use of these two paths.
When the System Path is used:
•
A count of eight consecutive ZBSs is used to create a logic 0 SUSPEND Register
value.
•
The CLTAPC supplies the TAP.7 scan path and controls the drive of TDO(C), provided
it is not bypasses.
• The EPU supplies the TAP.7 scan path (a one bit bypass) when the CLTAPC is
bypassed.
•
Functions supporting Boundary Scan in a Star Scan Topology are enabled.
When the EPU Path is used:
• When the control level has not been locked, the TDO(C) signal remains high-
impedance.
•
The command control level may be created
•
When commands are used, the TDO(C) signal remains high-impedance except during
Shift-DR states within CR-Scans, and remains high impedance at other times.
•
Auxiliary scan paths may be accessed with control levels four and five.
60.6.2

EPU Registers

60.6.2.1 Global
A global register is a register whose value is stored at the same time and with the same
value as registers with the same name in all TAP.7 TAPCs sharing an external tool
connection. They are stored using TAP.7 TAPC commands dedicated for this purpose.
IEEE 1149.7 Compact JTAG Test Access Port Controller (CJTAG)
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