7906 datasheet(372/531 Pages) RENESAS

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DEBUG FUNCTION

7906 Group User’s Manual Rev.2.0

17-11

17.4 Out-of-address-area detection mode

17.4.2 Operations in out-of-address-area detection mode

➀ Setting the detect enable bit to “1” initiate to compare the contents of PG and PC with the contents of

the address compare registers 0 and 1.

➁ When an address less than the contents of the address compare registers 0 or larger than the one of

the address compare register 1 is detected, an address matching detection interrupt request occurs, and

then, this request will be accepted.

➂ Perform the necessary processing with an address matching detection interrupt routine.

➃ The contents of PG, PC, and PS at acceptance of the address matching detection interrupt request are

saved onto the stack area. Therefore, be sure to rewrite the above contents of PG and PC to a certain

return address, and return there by using the RTI instruction.

When an address matching detection interrupt request has been accepted, the interrupt disable flag (I) is

set to “1”; the processor interrupt priority level (IPL) does not change.

By setting the start address of the programming area into the address compare register 0 and the last

address of the programming area into the address compare register 1, a program runaway (in other words,

fetching op codes from the area out of the programming area) can be detected. If any program runaway

is detected and reset of the microcomputer is required, be sure to write “1” into the software reset bit (bit

6 at address 5E16) within an address matching detection interrupt routine.

Figure 17.4.2 shows an example of program runaway detection using the out-of-address-area detection

mode.

Fig. 17.4.2 Example of program runaway detection using out-of-address-area detection mode

TOP_PRG :

Start address of programming area

→ This address is to be set into the address compare register 0,

in advance.

END_PRG : Last address of programming area

→ This address is to be set into the address compare register 1,

in advance.

Note: A program runaway may affect the contents of the data bank register (DT), the direct page registers (DPRi) etc.

Therefore, the contents of these registers must be rewritten in order to write “1” to the software reset bit with an

addressing mode using DT, DPRi, etc.

Address matching detection

interrupt routine

RTI

Software reset bit

← 1 (Note)

(bit 6 at address 5E16)

The microcomputer

is reset.

00000016

TOP_PRG

END_PRG

FFFFFF16

Access to the area

out of the progra-

mming area

Access to the

area out of the

programming

area

Programming area

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