M37221M4H_15 Datasheet, PDF (76/114 Pages) Renesas Technology Corp – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER for VOLTAGE SYNTHESIZER with ON-SCREEN DISPLAY CONTROLLER

M37221M4H/M6H/M8H/MAH–XXXSP/FP M37221EASP/FP
8.12 SOFTWARE RUNAWAY DETECT FUNCTION
This microcomputer has a function to decode undefined instructions
to detect a software runaway.
When an undefined op-code is input to the CPU as an instruction
code during operation, the following processing is done.
➀ The CPU generates an undefined instruction decoding signal.
➁ The device is internally reset due to the undefined instruction de-
coding signal.
➂ As a result of internal reset, the same reset processing as in the
case of ordinary reset operation is done, and the program restarts
from the reset vector.
Note, however, that the software runaway detecting function cannot
be disabled.
φ
SYNC
Address
PC
?
01,S
01,S–1 01,S–2 FFFE16 FFFF16
ADH,
ADL
Data
?
PCH
Undefined instruction decoding signal
occurs.Internal reset signal occurs.
PCL
PS
ADL
ADH
Reset sequence
: Undefined instruction decode
? : Invalid
PC : Program counter
S : Stack pointer
ADL, ADH: Jump destination address of reset
Fig. 8.12.1 Sequence at Detecting Software Runaway Detection
Rev.1.00 Oct 01, 2002 page 74 of 110
REJ03B0134-0100Z