MPC555
/
MPC556
IEEE 1149.1-COMPLIANT INTERFACE (JTAG)
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
22-3
22.3 Operating Frequency
The TCK frequency must be between 5 MHz and 10 MHz. This pin is internally driven
to a low value when disconnected.
22.4 TAP Controller
TRST is used to reset the TAP controller asynchronously. The TRST pin ensures that
the JTAG logic does not interfere with the normal operation of the chip. This pin is op-
tional in the JTAG specification.
The TAP controller changes state either on the rising edge of TCK or when TRST is
asserted.
The TDO signal remains in a high-impedance state except during the Shift-DR or Shift-
IR controller states. During these controller states, TDO is updated on the falling edge
of TCK.
The TAP controller states are designed to meet the IEEE 1149.1 standard. Refer to
Table 22-1 JTAG Interface Pin Descriptions
Signal
Name
Input/
Output (I/O)
Internal Pull-Up/
Pull-Down Provided
Description
TDI
Input
Pull-up
Test data input pin. Sampled on the rising edge of TCK. Has a
pull-up resistor.
TDO
Output
None
Test data output pin. Actively driven during the Shift-IR and Shift-
DR controller states. Changes on the falling edge of TCK. Can
be placed in high-impedance state.
TMS
Input
Pull-up
Test mode select pin. Sampled on the rising edge of TCK to se-
quence the test controller’s state machine. Has a pull-up resis-
tor.
TCK
Input
Pull-down
Test clock input to synchronize the test logic. Has a pull-down re-
sistor.
TRST
Input
Pull-up
TAP controller asynchronous reset. Provides initialization of the
TAP controller and other logic as required by the standard. Has
a pull-up resistor.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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