Freescale Semiconductor MPC8260 PowerQUICC II Family Reference Manual page 538

IEEE 1149.1 Test Access Port
from the shift register to the parallel outputs during the update-IR controller state. The four bits are used
to decode the five unique instructions listed in
Code
B7 B6 B5 B4 B3 B2 B1 B0
0 0 0 0 0
1 1 0 0 0
1 1 1 1 1
13-6
Table 13-2. Instruction Decoding
1
Instruction
0 0 0 EXTEST
0 0 0 SAMPLE/
PRELOAD
1 1 1 BYPASS
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Table 13-2.
External test. Selects the 475-bit boundary scan register.
EXTEST also asserts an internal reset for the PowerQUICC II's
system logic to force a known beginning internal state while
performing external boundary scan operations. By using the
TAP, the register is capable of scanning user-defined values
into the output buffers, capturing values presented to input
pins, sampling this data into the boundary scan register (device
revision B.3 and later), and controlling the output drive of
three-state output or bi-directional pins. For more details on the
function and use of EXTEST, refer to the IEEE 1149.1
standard.
Initializes the boundary scan register output cells before the
selection of EXTEST. This initialization ensures that known
data appears on the outputs when entering an EXTEST
instruction. SAMPLE/PRELOAD also provides a chance to
obtain a snapshot of system data and control signals.
NOTE: Since there is no internal synchronization between the
TCK and CLKOUT, the user must provide some form of
external synchronization between the JTAG operation at TCK
frequency and the system operation CLKOUT frequency to
achieve meaningful results.
The BYPASS instruction creates a shift register path from TDI
to the bypass register and, finally, to TDO, circumventing the
475-bit boundary scan register. This instruction is used to
enhance test efficiency when a component other than the
PowerQUICC II becomes the device under test. It selects the
single-bit bypass register as shown below.
Shift DR
G1
0
1
MUX
From TDI
1
When the bypass register is selected by the current instruction,
the shift register stage is cleared on the rising edge of TCK in
the capture-DR controller state. Thus, the first bit to be shifted
out after selecting the bypass register is always a logic zero.
Description
D
C
Clock DR
Freescale Semiconductor
To TDO