HD6432351 datasheet(96/1025 Pages) RENESAS

96 / 1025 page

Section 2 CPU

Rev. 3.00 Sep 15, 2006 page 62 of 988

REJ09B0330-0300

(2) Reset Exception Handling

After the

RES pin has gone low and the reset state has been entered, when RES goes high again,

reset exception handling starts. The CPU enters the power-on reset state when the NMI pin is high,

or the manual reset state when the NMI pin is low. When reset exception handling starts the CPU

fetches a start address (vector) from the exception vector table and starts program execution from

that address. All interrupts, including NMI, are disabled during reset exception handling and after

it ends.

(3) Traces

Traces are enabled only in interrupt control mode 2. Trace mode is entered when the T bit of EXR

is set to 1. When trace mode is established, trace exception handling starts at the end of each

instruction.

At the end of a trace exception-handling sequence, the T bit of EXR is cleared to 0 and trace mode

is cleared. Interrupt masks are not affected.

The T bit saved on the stack retains its value of 1, and when the RTE instruction is executed to

return from the trace exception-handling routine, trace mode is entered again. Trace exception-

handling is not executed at the end of the RTE instruction.

Trace mode is not entered in interrupt control mode 0, regardless of the state of the T bit.

(4) Interrupt Exception Handling and Trap Instruction Exception Handling

When interrupt or trap-instruction exception handling begins, the CPU references the stack pointer

(ER7) and pushes the program counter and other control registers onto the stack. Next, the CPU

alters the settings of the interrupt mask bits in the control registers. Then the CPU fetches a start

address (vector) from the exception vector table and program execution starts from that start

address.

Figure 2.16 shows the stack after exception handling ends.

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