24-2
MPC565/MPC566 Reference Manual
MOTOROLA
IEEE 1149.1 Test Access Port
IEEE1149.1 Compatibility Exceptions
The MPC565 enters JTAG mode by going through a standard device reset sequence
with a specific configuration word applied to the databus. Once JTAG has been
entered, the MPC565 remains in JTAG mode until another reset sequence is applied
to exit JTAG mode, or the device is powered down.
The JTAG output port, “tdo_dsdo” is configured with a weak pull-up when its output
drivers are disabled, rather than being tri-stated.
The TAP consists of five dedicated signal pins, a 16-state TAP controller, and two test data
registers. A boundary scan register links all device signal pins into a single shift register.
The test logic implemented utilizes static logic design. The MPC565/MPC566
implementation provides the capability to:
1. Perform boundary scan operations to test circuit-board electrical continuity.
2. Bypass the MPC565/MPC566 for a given circuit-board test by effectively reducing
the boundary scan register to a single cell.
3. Sample the MPC565/MPC566 system pins during operation and transparently shift
out the result in the boundary scan register.
4. Disable the output drive to pins during circuit-board testing.
NOTE
Certain precautions must be observed to ensure that the IEEE
1149.-like test logic does not interfere with nontest operation.
24.2.1 Overview
An overview of the MPC565/MPC566 scan chain implementation is shown in
Figure 24-2.The MPC565/MPC566 implementation includes a TAP controller, a 4-bit instruction
register, and two test registers (a one-bit bypass register and a 520-bit boundary scan
register). This implementation includes a dedicated TAP consisting of the following
signals:
TCK — a test clock input to synchronize the test logic. (with an internal pull-down
resistor)
TMS — a test mode select input (with an internal pullup resistor) that is sampled on
the rising edge of TCK to sequence the TAP controller’s state machine.
TDI — a test data input (with an internal pullup resistor) that is sampled on the rising
edge of TCK.
TDO — a three-state test data output that is actively driven in the shift-IR and
shift-DR controller states. TDO changes on the falling edge of TCK. (This pin also
has a weak pull-up that is active when output drivers are disabled, except during a
HI-Z instruction).