6-10
MC68330 USER’S MANUAL
MOTOROLA
The MC68330 includes on-chip circuitry to detect the initial application of power to the
device. Power-on reset (POR), the output of this circuitry, is used to reset both the system
and IEEE 1149.1 logic. The purpose for applying POR to the IEEE 1149.1 circuitry is to
avoid the possibility of bus contention during power-on. The time required to complete
device power-on is power-supply dependent. However, the IEEE 1149.1 TAP controller
remains in the test-logic-reset state while POR is asserted. The TAP controller does not
respond to user commands until POR is negated.
The MC68330 features a low-power stop mode, which is invoked using a CPU
instruction called LPSTOP. The interaction of the IEEE 1149.1 interface with low-power
stop mode is as follows:
1. Leaving the TAP controller test-logic-reset state negates the ability to achieve
minimal power consumption, but does not otherwise affect device functionality.
2. The TCK input is not blocked in low-power stop mode. To consume minimal
power, the TCK input should be externally connected to VCC or ground.
3. The TMS and TDI pins include on-chip pullup resistors. In low-power stop
mode, these two pins should remain either unconnected or connected to VCC
to achieve minimal power consumption.
6.5 NON-IEEE 1149.1 OPERATION
In non-IEEE 1149.1 operation, there are two constraints. First, the TCK input does not
include an internal pullup resistor and should be pulled up externally to preclude mid-
level inputs. The second constraint is to ensure that the IEEE 1149.1 test logic is kept
transparent to the system logic by forcing the TAP controller into the test-logic-reset state,
using either of two methods. During power-up, POR forces the TAP controller into this
state. Alternatively, sampling TMS as a logic one for five consecutive TCK rising edges
also forces the TAP controller into this state. If TMS either remains unconnected or is
connected to VCC, then the TAP controller cannot leave the test-logic-reset state,
regardless of the state of TCK.