MOTOROLA
MC68341 USER’S MANUAL
10-11
During the capture-IR controller state, the parallel inputs to the instruction shift register are
loaded with the standard 2-bit binary value (01) into the two least significant bits and the
loss-of-crystal (LOC) status signal into bit 2. The parallel outputs, however, remain
unchanged by this action since an update-IR signal is required to modify them.
The LOC status bit of the instruction register indicates whether an internal clock is
detected when operating with a crystal clock source. The LOC bit is clear when a clock is
detected and set when it is not. The LOC bit is always clear when an external clock is
used. The LOC bit can be used to detect faulty connectivity when a crystal is used to clock
the device.
10.4.1 EXTEST (000)
The external test (EXTEST) instruction selects the 155-bit boundary scan register.
EXTEST asserts internal reset for the MC68341 system logic to force a predictable benign
internal state while performing external boundary scan operations.
By using the TAP, the register is capable of a) scanning user-defined values into the
output buffers, b) capturing values presented to input pins, c) controlling the direction of
bidirectional pins, and d) controlling the output drive of three-state output pins. For more
details on the function and uses of EXTEST, please refer to the IEEE 1149.1 document.
10.4.2 SAMPLE/PRELOAD (001)
The SAMPLE/PRELOAD instruction selects the 155-bit boundary scan register and
provides two separate functions. First, it provides a means to obtain a snapshot of system
data and control signals. The snapshot occurs on the rising edge of TCK in the capture-
DR controller state. The data can be observed by shifting it transparently through the
boundary scan register.
NOTE
Since there is no internal synchronization between the IEEE
1149.1 clock (TCK) and the system clock (CLKOUT), the user
must provide some form of external synchronization to achieve
meaningful results.
The second function of SAMPLE/PRELOAD is to initialize the boundary scan register
output bits prior to selection of EXTEST. This initialization ensures that known data will
appear on the outputs when entering the EXTEST instruction.
10.4.3 BYPASS (X1X, 101)
The BYPASS instruction selects the single-bit bypass register as shown in Figure 10-9.
This creates a shift-register path from TDI to the bypass register and, finally, to TDO,
circumventing the 155-bit boundary scan register. This instruction is used to enhance test
efficiency when a component other than the MC68341 becomes the device under test.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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