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R8C18 Datasheet(PDF) 97 Page - Renesas Technology Corp |
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R8C18 Datasheet(HTML) 97 Page - Renesas Technology Corp |
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97 / 257 page  R8C/18 Group, R8C/19 Group 12. Interrupts Rev.1.30 Apr 14, 2006 Page 82 of 233 REJ09B0222-0130 12.1.6.7 Saving a Register In the interrupt sequence, the FLG register and PC are saved to the stack. After an extended 16 bits, 4 high-order bits in the PC and 4 high-order (IPL) and 8 low-order bits in the FLG register, are saved to the stack, the 16 low-order bits in the PC are saved. Figure 12.7 shows the Stack State Before and After Acknowledgement of Interrupt Request. The other necessary registers are saved by a program at the beginning of the interrupt routine. The PUSHM instruction can save several registers in the register bank being currently used(1) with a single instruction. NOTE: 1. Selectable from registers R0, R1, R2, R3, A0, A1, SB, and FB. Figure 12.7 Stack State Before and After Acknowledgement of Interrupt Request The register saving operation, which is performed as part of the interrupt sequence, saved in 8 bits at a time in four steps. Figure 12.8 shows the Register Saving Operation. . Figure 12.8 Register Saving Operation Stack [SP] SP value before interrupt is generated Previous stack contents LSB MSB Address Previous stack contents m −4 m −3 m −2 m −1 m m+1 Stack state before interrupt request is acknowledged [SP] New SP value Previous stack contents LSB MSB Previous stack contents m m+1 Stack state after interrupt request is acknowledged PCL PCM FLGL FLGH PCH m −4 m −3 m −2 m −1 Stack Address PCH : 4 high-order bits of PC PCM : 8 middle-order bits of PC PCL : 8 low-order bits of PC FLGH : 4 high-order bits of FLG FLGL : 8 low-order bits of FLG NOTE: 1.When executing software number 32 to 63 INT instructions, this SP is specified by the U flag. Otherwise it is ISP. Stack Completed saving registers in four operations. Address [SP] −5 [SP] PCL PCM FLGL FLGH PCH (3) (4) (1) (2) Saved, 8 bits at a time Sequence in which order registers are saved NOTE: 1. [SP] indicates the initial value of the SP when an interrupt request is acknowledged. After registers are saved, the SP content is [SP] minus 4. When executing software number 32 to 63 INT instructions, this SP is specified by the U flag. Otherwise it is ISP. [SP] −4 [SP] −3 [SP] −2 [SP] −1 PCH : 4 high-order bits of PC PCM : 8 middle-order bits of PC PCL : 8 low-order bits of PC FLGH : 4 high-order bits of FLG FLGL : 8 low-order bits of FLG |
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