Bypass (B[3:0] = 1111); Dsp56300 Restrictions; Figure 11-5 Bypass Register - Motorola DSP56305 User Manual

JTAG Port

DSP56300 Restrictions

11.3.2.8

BYPASS (B[3:0] = 1111)

The BYPASS instruction selects the single-bit Bypass register, as shown in Figure 11-5.
This creates a shift-register path from TDI to the Bypass register, and finally to TDO,
circumventing the BSR. This instruction is used to enhance test efficiency when a
component other than the DSP56300 core-based device becomes the device under test.
When the Bypass register is selected by the current instruction, the shift-register stage is
set to a logic 0 on the rising edge of TCK in the Capture-DR controller state. Therefore,
the first bit shifted out after selecting the Bypass register is always a logic 0.
Shift DR
From TDI
11.4 DSP56300 RESTRICTIONS
The control afforded by the output enable signals using the BSR and the EXTEST
instruction requires a compatible circuit-board test environment to avoid
device-destructive configurations. The user must avoid situations in which the
DSP56300 core output drivers are enabled into actively driven networks. In addition, the
EXTEST instruction can be performed only after power-up or regular hardware reset
while EXTAL was provided. Then during the execution of EXTEST, EXTAL can remain
inactive.
There are two constraints related to the JTAG interface. First, the TCK input does not
include an internal pullup resistor and should not be left unconnected. The second
constraint is to ensure that the JTAG test logic is kept transparent to the system logic by
forcing the TAP into the Test-Logic-Reset controller state, using either of two methods.
During power-up, TRST must be externally asserted to force the TAP controller into this
state. After power-up is concluded, TMS must be sampled as a logic 1 for five
consecutive TCK rising edges. If TMS either remains unconnected or is connected to
V , then the TAP controller cannot leave the Test-Logic-Reset state, regardless of the
CC
state of TCK.
11-12
G1
0
1
Mux
1

Figure 11-5 Bypass Register

DSP56305 User's Manual
D
C
CLOCKDR
To TDO
AA0115
MOTOROLA