M68HC05E24/D2
3-5
MOTOROLA
3.3 EVS LIMITATIONS
This paragraph explains the limitations that apply to using your E24EM in an HC05EVS.
(These limitations apply regardless of the resident MCU.)
Limitation 1. CLI/RTI. You may not trace a clear interrupt mask (CLI) or return from
interrupt (RTI) instruction with an interrupt enabled and pending, due to MCU interrupt
handling. Attempting such a trace causes an interrupt in the monitor map; this forces a
software reset of the HC05EVS. User breakpoints remain in the user map as SWI instructions;
you must remove such SWI instructions.
Limitation 2. Branch. Do not trace a conditional branch instruction (such as BRCLR) that
branches to itself. As the monitor places an SWI instruction on the object of the branch, the
system never would execute the instruction. However, it would appear to you that the
instruction had executed. You may enter a G command while the PC points to this type of
instruction as long as the instruction is not a breakpoint address.
Limitation 3. IRQ/SWI. Whenever possible, avoid mixing interrupt requests (IRQs) and
user software interrupts (SWIs). This prevents a possible IRQ-SWI timing problem: a
concurrent hardware interrupt and SWI could cause an HC05EVS failure that could stop
program execution. To recover from such a failure (which occurs very infrequently,
statistically), press the master reset switch (SW3).
Limitation 4. Memory Map. You must be aware of the memory map of the MCU being
simulated; be sure to use only valid ROM locations. The HC05EVS does not provide
protection to limit user programs to the exact amount of MCU ROM available. (For
information about memory maps, consult the technical data book for the MCU.)
Limitation 5. COP. The computer operating properly (COP) update register serves as an
EPROM location for the resident MCU. Accordingly, the platform-board write-protect jumper
header must enable write protection. Otherwise, any writes to the COP update register change
the value stored in user pseudo ROM.
Freescale Semiconductor, I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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