System And Epu Paths - STMicroelectronics SPC572L series Reference Manual

IEEE 1149.7 Compact JTAG Test Access Port Controller (CJTAG)
Table 992. ZBS use state characteristics with both TAP.7 and other ZBS use
ZBSINH SUSPEND
0 0
0 1
1 0
1 1
60.6.5

System and EPU Paths

The System path is utilized when the external tool requires access to system (STL)
resources. This path is used when either the SUSPEND Register is a logic 1 or the ZBS
count is less than or equal to one. The EPU path is used otherwise.
The EPU scan path is constructed from five types of EPU scan paths:
•
Bypass – A 1-bit scan path
• Bit – Supports set and test bit operations (a 1-bit shift register)
•
String – Support 32-bit reads or 32-bit writes
• Enumerate – A 36-bit scan path that transports a TAPC address with T3 and above
TAP.7s
•
Auxiliary – An n-bit scan path that transports 1 – n bits using a conventional IEEE
1149.1 style DR-Scan path using Control Levels 4 and 5.
60.7 APU (Advanced Protocol Unit) Operation
60.7.1 Overview
The Advanced Protocol Unit (APU) is placed between the EPU and the RSU to create the
T4 TAP.7 controller. The APU delivers advanced capabilities with a number of operating
modes (new scan formats) that utilize the Standard Protocol and the Advanced Protocol in
both the narrow and wide T4 TAP.7 versions.
The APU enables scan transfers with two signals by serializing the information related to a
TAPC state machine state. It provides a number of serialization formats to balance scan
flexibility and scan performance. It multiplexes the use of the TMSC signal for T4 TAP.7
controller functions. The serialization is bypassed to provide T3 TAP.7 capability.
With a wide TAP.7, the chip architect may choose to implement the TDIC and TDOC signal
functions as fixed functionality (the T3 TDIC and TDOC functions) or as programmable
between the T3 TDIC and TDOC signal functions and an alternate function using a TAP.7
controller register. In this case, the default signal function may be either of the
programmable choices. Programmable TDIC and TDOC functionality provides a means to
fully utilize these signals in any scan topology as the T3 TAP.7 functionality is fully
supported.
The entire EPU infrastructure (i.e., ZBS detection, control-level management, and command
generation) is utilized when either the Standard Protocol or the Advanced Protocol is used,
as these TAP.7 controller attributes are controlled entirely from the TAPC state machine
1778/2058
EPU operating ZBS use
state
RUNNING
SUSPENDED
STOPPED
Not possible
DocID027809 Rev 4
by:
EPU Command allocates to STL
STL ZBS sequence allocates to EPU
STL Test-Logic-Reset state allocates to EPU
RM0400
Until