20-4
MCF5249UM
MOTOROLA
TAP Controller
operations occur. TMS has an internal pullup so that if it is not driven low, its value will default to a logic
level of 1. However, if TMS will not be used, it should be tied to VDD. This pin also signals a hardware
breakpoint to the processor when in the debug mode.
20.2.4
TEST DATA INPUT/DEVELOPMENT SERIAL INPUT - (TDI/DSI)
This is a dual-function pin. If TEST[3:0] = 0001, then DSI is selected. If TEST[3:0] = 0000, then TDI is
selected. When used as TDI, this input signal provides the serial data port for loading the various JTAG
shift registers composed of the boundary scan register, the bypass register, and the instruction register.
Shifting in of data depends on the state of the JTAG controller state machine and the instruction currently
in the instruction register. This data shift occurs on the rising edge of TCK. TDI also has an internal pullup
so that if it is not driven low its value will default to a logic level of 1. However, if TDI will not be used, it
should be tied to VDD.
This pin also provides the single-bit communication for the debug module commands.
20.2.5
TEST DATA OUTPUT/DEVELOPMENT SERIAL OUTPUT - (TDO/DSO)
This is a dual-function pin. When TEST[3:0] = 0001, then DSO is selected. When TEST[3:0] = 0000, TDO
is selected. When used as TDO, this output signal provides the serial data port for outputting data from the
JTAG logic. Shifting out of data depends on the state of the JTAG controller state machine and the
instruction currently in the instruction register. This data shift occurs on the falling edge of TCK. When TDO
is not outputting test data, it is three-stated. TDO can also be placed in three-state mode to allow bussed
or parallel connections to other devices having JTAG.
20.3
TAP CONTROLLER
The state of TMS at the rising edge of TCK determines the current state of the TAP controller. There are
basically two paths that the TAP controller can follow: The first, for executing JTAG instructions; the
second, for manipulating JTAG data based on the JTAG instructions. The various states of the TAP
controller are shown in Figure 20-2. For more detail on each state, refer to the IEEE 1149.1A Standard
JTAG document.
Note: From any state that the TAP controller is in, Test-Logic-Reset can be entered if
TMS is held high for at least five rising edges of TCK.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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