Figure 1033.Dr_Scan Sequence Used For Command Creation - STMicroelectronics SPC572L series Reference Manual

IEEE 1149.7 Compact JTAG Test Access Port Controller (CJTAG)
60.6.3.1 Two Part Commands
TAP.7 controller commands are 10-bit values. The 10-bit commands are created by two
consecutive DR-Scans when the control level is locked at the command control level (two).
The first DR-Scan provides a five-bit command opcode. The second DR-Scan provides a
five-bit operand. These two scans are called the command part one (CP1) and command
part two (CP2), respectively. A command created entirely with these two scans is called a
two-part command.
60.6.3.2 Three Part Commands
Some commands are used to send and/or receive data values other than values embedded
in the command's operand. These commands are called three-part commands. With these
commands, CP1 and CP2 are followed by an additional DR-Scan to transport a data value
to or from an EPU scan path. When used for this purpose, the DR-Scan is called a Control
Register Scan (CR-Scan). The CR-Scan is a minimum of zero bits in length with there being
no maximum length. The CR-Scan path is described in SECTION.
60.6.3.3 Command Sequence
The two 5-bit values concatenated to create the 10-bit command represent the number of
Shift-DR states between the Capture-DR and Update-DR states of CP1 and CP2. The count
within CP1 creates the MSBs of the command while the count within CP2 creates the LSBs
of the command. The command is decoded when the Update-DR state of the second DR-
Scan is reached. A determination as to whether the command is a two- or three-part
command is made at this point. The command format is shown in
The 10-bit command created by CP1 and CP2 determines the command's function and
whether the command is a two- or three-part command. If the command is a two part
command, the function specified by the command is performed when command part 2
completes. If the command is a three-part command, the DR-Scan following CP2 performs
a TAP.7 controller function designated by the 10-bit controller command. This DR-Scan is
called a Control-Register Scan (CR-Scan) and can be any length. A CR-Scan has many of
the attributes of the DR-Scan as it moves data between the external tool and TAP.7
controller and accesses various EPU scan paths. There are many two part commands, but
only three three-part commands, each having a special purpose.
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Figure 1033. DR_Scan sequence used for command creation
st nd
1 DR Scan 2
creates
Op-code Operand
Command part 1 Command part 2
All Commands
TDO(C) remains high impedance
DocID027809 Rev 4
DR Scan
creates Accesses an EPU scan path
Three-part Commands Only
TDO(C) drive is requested
Time
Figure 1033.
rd
3 DR Scan
CR-Scan
Command part 3
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