R8CSLASH20 datasheet(114/501 Pages) RENESAS

114 / 501 page

R8C/20 Group, R8C/21 Group

12. Interrupts

Rev.2.00 Aug 27, 2008

Page 98 of 458

REJ09B0250-0200

12.1.6.7

Saving a Register

In the interrupt sequence, the FLG register and PC are saved to the stack.

After 4 high-order bits in the PC and 4 high-order (IPL) and 8 low-order bits in the FLG register, extended to

16 bits, are saved to the stack, the 16 low-order bits in the PC are saved.

Figure 12.8 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 1 instruction.

NOTE:

1. Selectable from the R0, R1, R2, R3, A0, A1, SB and FB registers.

Figure 12.8

Stack State Before and After Acknowledgement of Interrupt Request

The register saving operation which is performed in the interrupt sequence is saved in 8 bits every 4 steps.

Figure 12.9 shows the Register Saving Operation.

Figure 12.9

Stack

[SP]

SP value before

interrupt is generated

Content of previous stack

LSB

MSB

Address

Content of previous stack

−4

−3

−2

−1

m+1

Stack state before interrupt request

is acknowledged

[SP]

New SP value

Content of previous stack

LSB

MSB

Content of previous stack

m+1

Stack state after interrupt request

is acknowledged

PCL

PCM

FLGL

FLGH

PCH

−4

−3

−2

−1

Stack

Address

PCH

: High-order 4 bits of PC

PCM

: Middle-order 8 bits of PC

PCL

: Low-order 8 bits of PC

FLGH

: High-order 4 bits of FLG

FLGL

: Low-order 8 bits of FLG

NOTE:

1. When executing the 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 interrupt request is acknowledged.

After registers are saved, the SP content is [SP] minus 4.

When executing the

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

: High-order 4 bits of PC

PCM

: Middle-order 8 bits of PC

PCL

: Low-order 8 bits of PC

FLGH

: High-order 4 bits of FLG

FLGL

: Low-order 8 bits of FLG

R8C/20 Datasheet(PDF) 114 Page - Renesas Technology Corp

R8C/20 Datasheet(HTML) 114 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL