Z8 Encore!® Motor Control Flash MCUs
Product Specification
246
abled during critical sections of code where interrupts do not occur (such as adjusting the
stack pointer or modifying shared data).
Host software can poll the IDLE bit of the OCDSTAT register to determine if the OCD is
looping on a BRK instruction. When software wants to stop the CPU on the BRK instruc-
tion on which it is looping, software must not set the DBGMODE bit of the OCDCTL reg-
ister. The CPU may have vectored to an interrupt service routine. Instead, software clears
the BRKLP bit. This allows the CPU to finish the interrupt service routine it may be in and
return to the BRK instruction. When the CPU returns to the BRK instruction on which it
was previously looping, it automatically sets the DBGMODE bit and enters DEBUG
mode.
The majority of the OCD commands remain disabled when the eZ8 CPU is looping on a
BRK instruction. The eZ8 CPU must be in DEBUG mode before these commands can be
issued.
Break Points in Flash Memory
The BRK instruction is Op Code 00h, which corresponds to the fully programmed state of
a byte in Flash memory. To implement a break point, write 00hto the appropriate address,
overwriting the current instruction. To remove a break point, erase the corresponding page
of Flash memory and reprogram with the original data.
OCDCNTR Register
The On-Chip Debugger contains a multipurpose 16-bit Counter Register. It can be used
for the following:
•
•
•
Count system clock cycles between break points
Generate a BRK when it counts down to 0
Generate a BRK when its value matches the Program Counter
When configured as a counter, the OCDCNTR register starts counting when the On-Chip
Debugger leaves DEBUG mode and stops counting when it enters DEBUG mode again or
when it reaches the maximum count of FFFFh. The OCDCNTR register automatically
resets itself to 0000hwhen the OCD exits DEBUG mode if it is configured to count clock
cycles between break points.
If the OCDCNTR Register is configured to generate a BRK when it counts down to zero,
it will not be reset when the CPU starts running. The counter will start counting down
toward zero once the On-Chip debugger leaves DEBUG mode. If the On-Chip Debugger
enters DEBUG mode before the OCDCNTR register counts down to zero, the OCDCNTR
will stop counting.
If the OCDCNTR register is configured to generate a BRK when the program counter
matches the OCDCNTR register, the OCDCNTR register will not be reset when the CPU
On-Chip Debugger
P R E L I M I N A R Y
PS024604-1005
ZILOG [ ZILOG, INC. ]
