Central Processing Unit
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
3-19
3.7.6
Link Register (LR)
The link register (LR), SPR 8, supplies the branch target address for the branch conditional to link register
(bclrx) instruction, and can be used to hold the logical address of the instruction that follows a branch and
link instruction.
Note that although the two least-significant bits can accept any values written to them, they are ignored
when the LR is used as an address.
Both conditional and unconditional branch instructions include the option of placing the effective address
of the instruction after the branch instruction in the LR. This is done regardless of whether the branch is
taken.
3.7.7
Count Register (CTR)
The count register (CTR), SPR 9, is used to hold a loop count that can be decremented during execution
of branch instructions with an appropriately coded BO field. If the value in CTR is 0 before being
decremented, it is –1 afterward. The count register provides the branch target address for the branch
conditional to count register (bcctrx) instructio
2
CA
Carry (CA). In general, the carry bit is set to indicate that a carry out of bit 0 occurred during
execution of an instruction. Add carrying, subtract from carrying, add extended, and subtract
from extended instructions set CA if there is a carry out of bit 0, and clear it otherwise. The CA
bit is not altered by compare instructions or other instructions that cannot carry, except that shift
right algebraic instructions set the CA bit to indicate whether any ‘1’ bits have been shifted out
of a negative quantity.
3:24
—
Reserved
25:31
BYTES
This field specifies the number of bytes to be transferred by a Load String Word Indexed (lswx)
or Store String Word Indexed (stswx) instruction.
MSB
0
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
LSB
31
Field
Branch Address
Reset
Unchanged
Addr
SPR 8
Figure 3-9. Link Register (LR)
MSB
0
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
LSB
31
Field
Loop Count
Reset
Unchanged
Addr
SPR 9
Figure 3-10. Count Register (CTR)
Table 3-10. Integer Exception Register Bit Descriptions
Bits
Name
Description
Summary of Contents for MPC561
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