System Development and Debugging
MPC885 PowerQUICC Family Reference Manual, Rev. 2
53-28
Freescale Semiconductor
Figure 53-11. Enabling Clock Mode after Reset
Since DSDI is used to select the development port clock scheme, it is necessary to prevent any transitions
on DSDI during clock mode select. The port will not begin scanning for the start bit of a serial transmission
until 16 clocks after the negation of SRESET. If DSDI is asserted 16 clocks after SRESET negates, the
port waits until DSDI is negated to begin scanning for the start bit.
53.3.2.4
Development Port Serial Communications–Trap Enable Mode
When not in debug mode, the development port begins communicating by setting DSDO (the msb of the
35-bit development port shift register) low to indicate that all activity related to the previous transmission
is complete and that a new transmission can begin. The start of a serial transmission from an external
development tool to the development port is signaled by a start bit. A mode bit in the transmission defines
it as either a trap enable mode transmission or a debug mode transmission. If the mode bit is set, the
transmission will be 10 bits long and only seven data bits will be shifted into the shift register. These seven
bits will be latched into the TECR. A control bit determines whether the data is latched into the trap enable
and VSYNC bits of the TECR or into the breakpoints bits of the TECR.
53.3.2.4.1
Serial Data Into Development Port
The development port shift register is 35 bits wide, but trap enable mode transmissions only use 10 of the
35 bits as the following—the start/ready bit, a mode/status bit, a control/status bit, and the 7
least-significant data bits.
DSDI
CLKOUT
SRESET
DSDI is used after SRESET negation to select clock mode.
CLKEN
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
If DSDI is high, self-clocked mode is selected first start bit detected after DSDI negation.
If DSDI is slow, the internal asynchronous clock enable signal asserts 8 clocks after SRESET negation.
This enables asynchronous clock mode.
Summary of Contents for PowerQUICC MPC870
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