
MOTOROLA
8-26
DEVELOPMENT SUPPORT
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RCPU
REFERENCE MANUAL
8.3.2.1 Development Port Shift Register
The development port shift register is a 35-bit shift register. Instructions and data
are shifted into it serially from DSDI. These instructions or data are then transferred
in parallel to the processor or the trap enable control register (TECR).
When the processor enters debug mode, it fetches instructions from the develop-
ment port shift register. These instructions are serially loaded into the shift register
from DSDI.
When the processor is in debug mode, data is transferred to the CPU by shifting it
into the shift register. The processor then reads the data as the result of executing
a “move from special purpose register DPDR” (development port data register) in-
struction.
In debug mode, data is also parallel loaded into the development port shift register
from the CPU by executing a “move to special purpose register DPDR” instruction.
It is then shifted out serially to PLLL/DSDO.
8.3.2.2 Trap Enable Control Register
The trap enable control register (TECR) is a nine-bit register that is loaded from the
development port shift register. The contents of the TECR are used to drive the six
trap enable signals, the two breakpoint signals, and the VSYNC signal to the pro-
cessor. Trap-enable transmissions to the development port cause the appropriate
bits of the development port shift register to be transferred to the control register.
8.3.3 Development Port Clock Mode Selection
All of the development port serial transmissions are clocked transmissions. The
transmission clock can be either synchronous or asynchronous with the system
clock (CLKOUT). The development port supports three methods for clocking the
serial transmissions. The first method allows the transmission to occur without be-
ing externally synchronized with CLKOUT but at more restricted data rates. The
two faster communication methods require the clock and data to be externally syn-
chronized with CLKOUT.
The first clock mode is called
asynchronous clocked
since the input clock (DSCK)
is asynchronous with CLKOUT. The input synchronizers on the DSCK and DSDI
pins sample the inputs to ensure that the signals used internally have no metasta-
ble oscillations. To be sure that data on DSDI is sampled correctly, transitions on
DSDI must occur a setup time ahead of the rising edge of DSCK. Data on DSDI
must also be held for one CLKOUT cycle plus one hold time after the rising edge
of DSCK. This ensures that after the signals have passed through the input syn-
chronizers, the data will be valid at the rising edge of the serial clock even if DSCK
and DSDI do not meet the setup and hold time requirements of the pins.
Asynchronous clocked mode allows communications with the port from a develop-
ment tool that does not have access to the CLKOUT signal or where the CLKOUT
signal has been delayed or skewed. Because of the asynchronous nature of the
inputs and the setup and hold time requirements on DSDI, this clock mode must
be clocked at a frequency less than or equal to one third of CLKOUT.
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Freescale Semiconductor, Inc.
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