Figure 1038.Serialization And De-Serialization Of Scan Packet Information - STMicroelectronics SPC572L series Reference Manual

IEEE 1149.7 Compact JTAG Test Access Port Controller (CJTAG)
formats. Some scan formats send less information and consequently take fewer TCKC
periods.
Figure 1038. Serialization and De-serialization of Scan Packet Information
characteristics
SYS_TCK
SYS_TMS
SYS_TDO
In order to produce comparable TAPC state machine state rates with a TAP.1 and TAP.7
controller:
•
Full-cycle timing between the external tool and TAP.7 allows operation at higher TCKC
frequencies.
•
The number of bits transferred to advance a TAPC state machine is minimized.
(reaching as few as one for some scan formats.)
The TAP.7 controller provides both full-cycle bit timing (falling TCKC edge to falling TCKC
edge) and half-cycle bit timing (falling TCKC edge to rising TCKC edge), with a TAP.7
register used to define the type of timing used. Half-cycle timing is used as the default
following a TAP.7 controller reset. The TCKC frequency is reduced to accommodate half-
cycle timing.
With full-cycle timing, the TMSC input and output data are both output with and sampled
with the falling edge of the TCKC. This means that the entire TCKC period may be spent
transferring a bit from the external tool to the TAP.7 or vice-versa. The TCKC frequency can
therefore be maximized when full-cycle timing is used. With half-cycle timing, the APU
samples the TMSC input data with the rising edge of the TCKC and outputs TMSC data with
the falling edge of TCKC.
Minimizing the number of bits transferred per TAPC state machine state is affected by a
number of factors. The information that must be transferred per TAPC state machine state
varies for different test and debug applications. Also, with some test and debug applications,
all TAPC state machine states do not require that the same amount of information be
transferred. This is especially true with debug applications where specialized use of the TAP
is more likely.
1784/2058
Information exchange for
One TAP controller state
TCK
TMSC nTDI
Reserved for
Drive
external tool drive
SYS_TDI
DocID027809 Rev 4
TMS TDO
Reserved for
TS drive
external tool drive
State[n]
State[n]
nTDII TMS
Reserved for Reserved for
external tool drive external tool drive
State[n]
RM0400