7220 Datasheet, PDF (117/303 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER

FUNCTIONAL DESCRIPTION
2.13 Software runaway detect function
2.13 Software runaway detect function
The M37221M6-XXXSP/FP 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 of the M37221M6-
XXXSP/FP, the following processing is done.
ΠThe CPU generates an undefined instruction decoding signal.
 The device is internally reset because of occurrence of the undefined instruction decoding signal.
Ž 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 invalid.
φ
SYNC
Address
PC
?
01,S
01,S–1 01,S–2 FFFE16 FFFF16
ADH,
ADL
Data
?
PCH
PCL
PS
ADL
ADH
Undefined instruction decoding signal occurs.
Internal reset signal occurs.
Reset sequence
: Undefined instruction decode
? : Invalid
PC : Program counter
S : Stack pointer
ADL, ADH : Jump destination address of reset
Fig. 2.13.1 Sequence at detecting software runaway detection
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7220 Group User’s Manual