Motorola M68000 User Manual download pdf (Page 75)

Integer Instructions

4-90 M68000 FAMILY PROGRAMMER’S REFERENCE MANUAL MOTOROLA

DBcc Test Condition, Decrement, and Branch DBcc

(M68000 Family)

Operation: If Condition False

Then (Dn – 1 → Dn; If Dn ≠ – 1 Then PC + d

→ PC)

Assembler

Syntax: DBcc Dn, < label >

Attributes: Size = (Word)

Description: Controls a loop of instructions. The parameters are a condition code, a data

termination; if it is true, no operation is performed. If the termination condition is not

true, the low-order 16 bits of the counter data register decrement by one. If the result

is – 1, execution continues with the next instruction. If the result is not equal to – 1,

execution continues at the location indicated by the current value of the program

counter plus the sign-extended 16-bit displacement. The value in the program counter

is the address of the instruction word of the DBcc instruction plus two. The

displacement is a twos complement integer that represents the relative distance in

bytes from the current program counter to the destination program counter. Condition

code cc speciﬁes one of the following conditional tests (refer to Table 3-19 for more

information on these conditional tests):

Condition Codes:

Not affected.

Mnemonic Condition Mnemonic Condition

CC(HI) Carry Clear LS Low or Same

CS(LO) Carry Set LT Less Than

EQ Equal MI Minus

F False NE Not Equal

GE Greater or Equal PL Plus

GT Greater Than T True

HI High VC Overflow Clear

LE Less or Equal VS Overflow Set

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Motorola M68000 User Manual Page 75