UM0434 datasheet(50/390 Pages) STMICROELECTRONICS

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UM0434

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4.6.2

Count register (CTR)

CTR can be used to hold a loop count that can be decremented and tested during execution

of branch instructions that contain an appropriately encoded BO field. If the CTR value is 0

before it is decremented, it is –1 afterward. The entire CTR can hold the branch target

address for a Branch Conditional to CTR (bcctr

x) instruction.

4.6.3

Link register (LR)

The link register, shown in

Table 20, provides the branch target address for the branch

conditional to LR instructions, and it holds the return address after branch and link

instructions.

n[2]

4 * cr0 + eq (or eq)

4 * cr1 + eq

4 * cr2 + eq

4 * cr3 + eq

4 * cr4 + eq

4 * cr5 + eq

4 * cr6 + eq

4 * cr7 + eq

000

001

010

011

100

101

110

111

Equal (EQ).

For integer compare instructions: rA =

SIMM, UIMM, or rB.

n[3]

4 * cr0 + so (or so)

4 * cr1 + so

4 * cr2 + so

4 * cr3 + so

4 * cr4 + so

4 * cr5 + so

4 * cr6 + so

4 * cr7 + so

000

001

010

011

100

101

110

111

Summary overflow (SO).

For integer compare instructions, this is a

copy of XER[SO] at instruction completion.

Table 18.

CR setting for compare instructions (continued)

Bit

Bit Expression

CR Bits

Description

Book E

0–2

3–4

Table 19.

Count register (CTR)

Field

Count value

Reset

Undefined on

m_por assertion, unchanged on p_reset_b assertion

R/W

SPR

SPR 9

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