Development Capabilities and Interface
MOTOROLA
MPC823 USER’S MANUAL
20-31
DEVELOPMENT
20
CAPABILITIES
&
INTERFACE
The instructions or data are then transferred in parallel to the core and TECR. When the
processor enters debug mode it fetches instructions from the DPIR, which causes an access
to the development interface port shift register. These instructions are serially loaded into
the shift register from the DSDI using DSCK or CLKOUT as the shift clock. Similarly, data is
transferred to the core. Data is shifted into the shift register and read by the processor when
a “move from special-purpose register DPDR” instruction is executed. Data is also parallel
loaded into the development interface port shift register from the core by executing a “move
to special-purpose register DPDR” instruction. It is then serially shifted out to the DSDO pin
using DSCK or CLKOUT as the shift clock.
20.4.3.5.2 Trap Enable Control Register. The 9-bit trap enable control register (TECR) is
loaded from the development interface port shift register. The contents of the control register
drive the six trap enable signals, two breakpoint signals, and the VSYNC signal to the core.
The transfer data to trap enable control register commands are used to force the appropriate
bits to be transferred to this register. The trap enable control register is not accessed by the
core, but supplies signals to the core. The trap enable bits, VSYNC bit, and the breakpoint
bits of this register are loaded from the development interface port shift register as a result
of trap enable mode transmissions. The trap enable bits are reflected in the ICTRL and
information on the support registers.
20.4.3.5.3 Decoding the Development Interface Port Registers. The development
interface port shift register is selected when the core accesses the DPIR or DPDR registers.
Accesses to these two special-purpose registers occur in debug mode and appear on the
internal bus as an address and the assertion of an address attribute signal indicating that a
special-purpose register is being accessed. The DPIR is read by the core to fetch all
instructions when in debug mode. The DPDR is read and written to transfer data between
the core and external development tools. The DPIR and DPDR are pseudo-registers, so
decoding either of these registers causes the development interface port shift register to be
accessed. The debug mode logic knows whether the core is fetching instructions or reading
or writing data. A sequence error is signaled to the external development tool when the core
expected result and the GPR result do not match. An example of this would be when an
instruction is received instead of the expected data.
20.4.3.6 DEVELOPMENT PORT SERIAL COMMUNICATION. All serial transmissions
are synchronous, with respect to the transmission clock.
20.4.3.6.1 Clock Mode Selection. With respect to CLKOUT, the transmission clock can
either be synchronous or asynchronous. The development port has two methods that can
be used to clock serial transmissions. The first method allows the transmission to occur
without being externally synchronized to CLKOUT. In this mode, a serial clock DSCK must
be supplied to the MPC823. The other communication method requires data to be externally
synchronized with respect to CLKOUT.