C-2
MPC106 PCIB/MC User's Manual
MOTOROLA
C.1.1 JTAG Signals
The MPC106 provides five dedicated JTAG signals—test data input (TDI), test mode select
(TMS), test reset (TRST), test clock (TCK), and test data output (TDO). The TDI and TDO
signals are used to input and output instructions and data to the JTAG scan registers. The
boundary-scan operations are controlled by the TAP controller through commands received
by means of the TMS signal. Boundary-scan data is latched by the TAP controller on the
rising edge of the TCK signal. The TRST signal is specified as optional by the IEEE 1149.1
specification, and is used to reset the TAP controller asynchronously. The assertion of the
TRST signal at power-on reset assures that the JTAG logic does not interfere with the
normal operation of the MPC106.
Section 2.2.7, “IEEE 1149.1 Interface Signals,” provides additional detail about the
operation of these signals.
C.1.2 JTAG Registers and Scan Chains
The bypass, boundary-scan, and instruction JTAG registers and their associated scan chains
are implemented by the MPC106. These registers are mandatory for compliance with the
IEEE 1149.1 specification.
C.1.2.1 Bypass Register
The bypass register is a single-stage register used to bypass the boundary-scan latches of
the MPC106 during board-level boundary-scan operations involving components other
than the MPC106. The use of the bypass register reduces the total scan string size of the
boundary-scan test.
C.1.2.2 Boundary-Scan Registers
The JTAG interface provides a chain of registers dedicated to boundary-scan operations. To
be JTAG-compliant, these registers cannot be shared with any functional registers of the
MPC106. The boundary-scan register chain includes registers controlling the direction of
the input/output drivers, in addition to the registers reflecting the signal value received or
driven.
The boundary-scan registers capture the input or output state of the MPC106’s signals
during a Capture_DR TAP controller state. When a data scan is initiated following the
Capture_DR state, the sampled values are shifted out through the TDO output while new
boundary-scan register values are shifted in through the TDI input. At the end of the data
scan operation, the boundary-scan registers are updated with the new values during an
Update_DR TAP controller state.
Note that the LSSD_MODE signal (used for factory testing) is not included in the
boundary-scan register chain.