BDM/JTAG Signals
MOTOROLA
Signal Description
2-13
controller to the test logic reset state, causing the JTAG instruction register to choose the “bypass”
command. When this occurs, all the JTAG logic is benign and will not interfere with the normal functionality
of the MCF5249 processor. Although this signal is asynchronous, Motorola recommends that TRST make
only a 0 to 1 (asserted to negated) transition while TMS is held at a logic 1 value. TRST has an internal
pullup so that if it is not driven low its value will default to a logic level of 1. However, if TRST will not be
used, it can either be tied to ground or, if TCK is clocked, it can be tied to VDD. If it is tied to ground, it will
place the JTAG controller in the test logic reset state immediately. If it is tied to VDD, it will cause the JTAG
controller (if TMS is a logic 1) to eventually end up in the test logic reset state after 5 clocks of TCK.
This pin is also used as the development serial clock (DSCLK) for the serial interface to the Debug
Module.The maximum frequency for the DSCLK signal is 1/5 the BCLKO frequency.
2.20.3
TEST MODE SELECT/BREAK POINT
The TEST[3:0] signals determine the TMS/BKPT pin function. If TEST[3:0] =0001, the BKPT function is
selected. If TEST[3:0] = 0000, then the TMS function is selected. TEST[3:0] should not change while RSTI
= 1. When used as TMS, this input signal provides the JTAG controller with information to determine which
test operation mode should be performed. The value of TMS and current state of the internal 16-state
JTAG controller state machine at the rising edge of TCK determine whether the JTAG controller holds its
current state or advances to the next state. This directly controls whether JTAG data or instruction
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.
2.20.4
TEST DATA INPUT/DEVELOPMENT SERIAL INPUT
The TDI/DS 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.
2.20.5
TEST DATA OUTPUT/DEVELOPMENT SERIAL OUTPUT
The TDO/DSO 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. This signal also provides single-bit
communication for the debug module responses.
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Freescale Semiconductor, Inc.
For More Information On This Product,
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