MC68340 datasheet(387/441 Pages) FREESCALE

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9- 12

MC68340 USER’S MANUAL

MOTOROLA

The MC68340 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 MC68340 features a low-power stop mode that uses a CPU instruction called

LPSTOP. The interaction of the IEEE 1149.1 interface with LPSTOP 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 LPSTOP 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 LPSTOP mode, these two

pins should remain either unconnected or connected to VCC to achieve minimal

power consumption.

9.6 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-on, 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.

Freescale Semiconductor, Inc.

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MC68340 Datasheet(PDF) 387 Page - Freescale Semiconductor, Inc