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HTS Demo Kit V1.0 12/ 20 December 2007
7.4. Register Operation Limitations
Table 6-2 lists the limitations on register operation. The registers are inhibited from any modification. If
register contents are modified in any way, kernel operation cannot be guaranteed.
Table 7-2: Limitations on Register Operation
Register Name Restriction
User and Interrupt Stack Pointers RAM memory range 0B80H – 0BFFH is used by
the kernel. Do not set stacks in this area.
UART1 Transmit/Receive Mode Register
UART1 Transmit/Receive Control Register 0
UART1 Transmit/Receive Control Register 1
Do not change.
UART1 Interrupt Control Register 0 Do not change.
UART Transmit/Receive Control Register 2 Do not change bits 0 and 2.
UART1 Transmit Buffer Register Do not write to this register.
UART1 Receive Buffer Register Do not read this register.
Port 6 and Port 6 DDR To prevent changes on P6_4 data and direction,
use read-modify-write only instructions (BSET,
BCLR, AND, OR, etc.).
7.5. Limitations on Interrupts – Vectors that Reside in the Hardware Vector Table
Table 7-3 lists the limitations on hardware interrupt (i.e. fixed) vector addresses.
Table 7-3: Interrupt Vector Addresses
Interrupt Cause M16C/26A Vector Address Kit Specification
Undefined FFFDCh ~ FFFDFh User available
Overflow FFFE0h ~ FFFE3h User available
BRK Instruction FFFE4h ~ FFFE7h User inhibited
Address Match FFFE8h ~ FFFEBh User inhibited
Single-step FFFECh ~ FFFEFh User inhibited
Watchdog Timer FFFF0h ~ FFFF3h User available (Note 1)
DBC FFFF4h ~ FFFF7h User inhibited
NMI FFFF8h ~ FFFFBh User available
RESET FFFFCh ~ FFFFFh Reset vector (Note 2)
NOTES:
(1) The Watchdog Timer vector is shared with the oscillation stop and voltage detection interrupts.
The vector is available for oscillation stop and voltage detection interrupts, but you must avoid using
the vector for watchdog timer interrupts.
(2) The kernel transparently relocates the Reset vector to FFFD8h.
7.6. Stop or Wait Mode Limitations
The kernel cannot be run in STOP or WAIT modes. Do not use these modes when debugging your
program.
7.7. User Program’s Real-Time Capability (Very Important – Please Read)
Please be aware that while the kernel is in a “STOP” state, the hardware peripherals will continue to run.
Therefore, interrupts may not be serviced properly. In addition, the watchdog timer will not be serviced
and will likely time out if active.