Figure 1037.Scan Packet Sequence - STMicroelectronics SPC572L series Reference Manual

RM0400
or the TDIC and TDOC pins have an alternate function assigned to them), the APU provides
a logic 1 to the EPU for unsupported pin functions and ignores the EPU's TDO output data.
60.7.5.2 Scan Packet Active (SPA) Function
The Scan Control function is encapsulated within the Scan Packet Active (SPA) state. With
the Standard Protocol, the external tool and TAP.7 exchange the scan information
associated with a single TAPC state machine state in one TCK period using the TMS(C),
TDI(C), and TDO(C) pins. With the Advanced Protocol all or part of this information is
exchanged serially within a Scan Packet (SP) as shown in . There is a one to one
correspondence between SPs and TAPC state machine state changes, except when the
SPA state precedes the CPA state. In this case the SP preceding a CP does not advance
the TAPC state machine state.
A comparison of the parallel transfer of TAP information with the Standard Protocol and the
serialization and de-serialization of the TAP information using the TCKC and TMSC pins
with the Advanced Protocol is shown in FIGURE. The IEEE 1149.1 signals between the
EPU and STL are prefixed with SYS_.
The APU manages the serialization and de-serialization of the scan information. The APU
converts the TDI and TMS information within a Scan Packet (SP) into the TMS and TDI
information presented to the EPU. It converts the combination of the EPU TDO and EPU
TDO_OE signals into the TDO information in the same SP. If the EPU indicates that the
TDO pin drive is not enabled, logic 1 TDO data is created, otherwise the TDO data is the
supplied by either the EPU or STL.
Information within a Scan Packet is first passed from the external tool to the TAP.7 followed
by information passed from the TAP.7 to the external tool. In this example the scan format
specifies the exchange of the TMS, TDI, and TDO TAPC information. Each TAPC state
machine state takes three TCKC periods. Other scan formats specify the exchange of
different mixes of information. Control information is added with the most flexible scan
IEEE 1149.7 Compact JTAG Test Access Port Controller (CJTAG)
Figure 1037. Scan Packet sequence
TCKC
nTDI
TMS TDO
TMSC
TAPC
Run-Test/Idle
State
DocID027809 Rev 4
Scan Packet
nTDI nTDI
TMS TDO TMS
Select-DR Capture-DR
nTDI
TDO TMS TDO
Shift-DR
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