Development Capabilities and Interface
MOTOROLA
MPC823 USER’S MANUAL
20-29
DEVELOPMENT
20
CAPABILITIES
&
INTERFACE
20.4.3 The Development Interface Port
The development port provides a full-duplex serial interface for communications between
the internal development support logic and an external development tool. The relationship
of the development support logic to the rest of the core is illustrated in
Figure 20-5. Notice
that the development port support logic is shown as a separate block for clarity. It will be
implemented as part of the system interface unit module. The development interface port
contains the four pins:
Development serial clock
Development serial data in
Development serial data out
Freeze
20.4.3.1 DEVELOPMENT SERIAL CLOCK. The development serial clock (DSCK) pin is
used to shift data into and out of the development interface port shift register. At the same
time, the new most-significant bit of the shift register is presented to the development serial
data out (DSDO) pin. Future references to the DSCK signal imply the internally
synchronized value of the clock. The DSCK input must be driven either high or low at all
times and it not allowed to float. With a resistor, a typical target environment would pull this
input low.
The clock can be implemented as a free-running or gated clock. The shifting of data is
controlled by the ready and start signals, so the clock does not need to be gated with the
serial transmissions. The DSCK pin is used at reset to enable debug mode either
immediately following reset or to enter debug mode driving an event.
20.4.3.2 DEVELOPMENT SERIAL DATA IN. Data to be transferred into the development
interface port shift register is presented to the development serial data in (DSDI) pin by
external logic. When driven asynchronous with the system clock, the data presented to the
DSDI pin must be stable at setup time before the rising edge of DSCK and at hold time after
the rising edge of DSCK. When synchronously driven to the system clock, the data must be
stable on DSDI or a setup time before system clock output (CLKOUT) rising edge and a hold
time after the rising edge of CLKOUT. The DSDI pin is also used at reset to control the
overall chip configuration mode and determine the development port clock mode. Refer to
20.4.3.3 DEVELOPMENT SERIAL DATA OUT. The debug mode logic shifts data out of
the development interface port shift register using the development serial data out (DSDO)
pin. All transitions on DSDO are synchronous with DSCK or CLKOUT, depending on the
clock mode. Data will be valid at setup time before the rising edge of the clock and remains
valid at hold time after the rising edge of the clock. See
Table 20-10 for details about DSDO
data.