MPC555
/
MPC556
IEEE 1149.1-COMPLIANT INTERFACE (JTAG)
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
22-7
2. The TCK input is not blocked in low-power stop mode. To consume minimal
power, the TCK input should be externally connected to VDD or ground, al-
though TCK pin is internally connected to ground.
3. The TMS, TDI and TRST pins include on-chip pullup resistors. In low-power
stop mode, these three pins should remain either unconnected or connected to
VDD to achieve minimal power consumption.
NOTE
For proper reset of the scan chain test logic, the best approach is to
assert TRST at power on reset (PORESET).
22.8 Non-IEEE 1149.1-1990 Operation
In non-IEEE 1149.1-1990 operation, the IEEE 1149.1-1990 test logic must be kept
transparent to the system logic by forcing and holding the TAP controller into the
test-
logic-reset
controller state. There are two methods of forcing and holding the control-
ler to this state. The first is to assert the TRST signal, forcing the TAP into the
test-
logic-reset
controller state. The second is to provide at least five TCK pulses with
TMS held high.
The best approach is to connect a pull down resistor to TRST, or to connect it to
PORESET with a resistor. If bounday scan is required, the JTAG controller should
drive TRST to the negated state (“1” value) following PORESET.
22.9 Boundary Scan Register
The MPC555 / MPC556 scan chain implementation has a 346-bit boundary scan reg-
ister. This register contains bits for all device signal and clock pins and associated con-
trol signals. The XTAL, EXTAL and XFC pins are associated with analog signals and
are not included in the boundary scan register.
An IEEE-1149.1 compliant boundary scan register has been included on the MPC555
/ MPC556. This 346-bit boundary scan register can be connected between TDI and
TDO when EXTEST or SAMPLE/PRELOAD instructions are selected. This register is
used for capturing signal pin data on the input pins, forcing fixed values on the output
signal pins, and selecting the direction and drive characteristics (a logic value or high
impedance) of the bidirectional and three-state signal pins.
through
depict the various cell types.
F
re
e
sc
a
le
S
e
m
ic
o
n
d
u
c
to
r,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
c
.
..