UM0434 datasheet(47/390 Pages) STMICROELECTRONICS

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UM0434

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CR bits are grouped into eight 4-bit fields, CR0–CR7, which are set as follows:

●

Specified CR fields are set by a move to the CR from a GPR (mtcrf).

●

A specified CR field is set by a move to the CR from another CR field (mcrf), or from

the XER (mcrxr).

●

CR0 may be set as the implicit result of an integer instruction.

●

A specified CR field may be set as the result of either an integer or a floating-point

compare instruction (including SPE and SPFP compare instructions).

Instructions are provided to perform logical operations on individual CR bits and to test

individual CR bits.

Note:

Book E instructions that access CR bits, such as Branch Conditional (bc), CR logicals, and

Move to Condition Register Field (mtcrf), determine the bit position by adding 32 to the

value of the operand. For example, the BI operand accesses the bit BI + 32, as shown in

Table 16.

Table 15.

Condition register (CR)

35 36

39 40

43 44

47 48

51 52

55 56

59 60

Field

Reset

Undefined on

m_por assertion, unchanged on p_reset_b assertion

R/W R/W

Table 16.

BI operand settings for CR fields

Bits

Description

CR0[0]

00000

Negative (LT)—Set when the result is negative.

For SPE compare and test instructions:

Set if the high-order element of rA is equal to the high-order element of rB; cleared

otherwise.

CR0[1]

00001

Positive (GT)—Set when the result is positive (and not zero).

For SPE compare and test instructions:

Set if the low-order element of rA is equal to the low-order element of rB; cleared

otherwise.

CR0[2]

00010

Zero (EQ)—Set when the result is zero. For SPE compare and test instructions:

Set to the OR of the result of the compare of the high and low elements.

CR0[3]

00011

Summary overflow (SO). Copy of XER[SO] at the instruction’s completion.

For SPE compare and test instructions:

Set to the AND of the result of the compare of the high and low elements.

CR1[0]

00100

Negative (LT)—For SPE and SPFP compare and test instructions:

Set if the high-order element of rA is equal to the high-order element of rB; cleared

otherwise.

CR1[1]

00101

Positive (GT)—For SPE and SPFP compare and test instructions:

Set if the low-order element of rA is equal to the low-order element of rB; cleared

otherwise.

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