Extest (B[3:0] = 0000); Sample/Preload (B[3:0] = 0001); Idcode (B[3:0] = 0010) - Motorola DSP56305 User Manual

11.3.2.1

EXTEST (B[3:0] = 0000)

The external test (EXTEST) instruction selects the BSR. EXTEST also asserts internal reset
for the DSP56300 core system logic to force a predictable internal state while performing
external boundary scan operations.
By using the TAP, the BSR is capable of the following:
• Scanning user-defined values into the output buffers
• Capturing values presented to input signals
• Controlling the direction of bidirectional signals
• Controlling the output drive of tri-statable output signals
For more details on the function and use of the EXTEST instruction, please refer to the
IEEE 1149.1 document.
11.3.2.2

SAMPLE/PRELOAD (B[3:0] = 0001)

The SAMPLE/PRELOAD instruction 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 BSR.
Note: Since there is no internal synchronization between the JTAG clock (TCK) and
the system clock (CLK), the user must provide some form of external
synchronization to achieve meaningful results.
The second function of the SAMPLE/PRELOAD instruction is to initialize the BSR
output cells prior to selection of EXTEST. This initialization ensures that known data
appears on the outputs when entering the EXTEST instruction.
11.3.2.3

IDCODE (B[3:0] = 0010)

The IDCODE instruction selects the ID register. This instruction is provided as a public
instruction to allow the manufacturer, part number, and version of a component to be
determined through the TAP. Figure 11-4 shows the ID register configuration.
MOTOROLA DSP56305 User's Manual
JTAG Port
TAP Controller
11-9