Configuration Basics
Am186™CC/CH/CU Microcontrollers User’s Manual
2-3
After the processor executes an instruction, the value of the flags can be set to 1, cleared
or reset to 0, unchanged, or undefined. The term
undefined means that the flag value prior
to the execution of the instruction is not preserved, and that after the instruction is executed,
the value of the flag cannot be predicted.
Figure 2-2
Processor Status Flags Register
Bits 15–12, Reserved
Bit 11, Overflow Flag (OF): Set if the signed result cannot be expressed within the number
of bits in the destination operand; otherwise cleared.
Bit 10, Direction Flag (DF): When set, causes string instructions to auto-decrement the
appropriate index registers. When cleared, causes auto-increment.
Bit 9, Interrupt-Enable Flag (IF): When set, enables maskable interrupts to cause the
CPU to transfer control to a location specified by an interrupt vector. This flag is cleared
when the processor takes a hardware interrupt, or a trace interrupt, by using the CLI
instruction. For more information about hardware and software interrupts, see Chapter 7,
“Interrupts.”
Bit 8, Trace Flag (TF): When set, a trace interrupt occurs after instructions execute. TF is
cleared by the trace interrupt after the processor status flags are pushed onto the stack.
The trace service routine can continue tracing by popping the flags back with an interrupt
return (IRET) instruction.
Bit 7, Sign Flag (SF): Set equal to high-order bit of result (0 if 0 or positive, 1 if negative).
Bit 6, Zero Flag (ZF): Set if result is 0; otherwise cleared.
Bit 5, Reserved
Bit 4, Auxiliary Carry (AF): Set on carry from or borrow to the low-order four bits of the
AL general-purpose register; otherwise cleared.
Bit 3, Reserved
Bit 2, Parity Flag (PF): Set if low-order eight bits of result contain an even number of bits
set to 1; otherwise cleared.
Bit 1, Reserved
Bit 0, Carry Flag (CF): Set on high-order bit carry or borrow; otherwise cleared.
15
7
0
IF
TF
SF
ZF
Res
CF
PF
Reserved
Res
AF
Res
OF
DF
Содержание Am186 CC
Страница 1: ...Am186 CC CH CU Microcontrollers User s Manual Order 21914B...
Страница 4: ...iv Am186 CC CH CU Microcontrollers User s Manual...
Страница 18: ...Table of Contents xviii Am186 CC CH CU Microcontrollers User s Manual...
Страница 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
Страница 39: ...Architectural Overview Am186 CC CH CU Microcontrollers User s Manual 1 15 Figure 1 6 32 Channel Linecard CH CC...
Страница 40: ...Architectural Overview 1 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 86: ...System Overview 3 36 Am186 CC CH CU Microcontrollers User s Manual...
Страница 92: ...Emulator Support 4 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 112: ...DRAM Controller 6 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 134: ...Interrupts 7 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 186: ...Programmable I O Signals 9 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 200: ...Watchdog Timer 11 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 232: ...Asynchronous Serial Ports UARTs 13 24 Am186 CC CH CU Microcontrollers User s Manual...
Страница 242: ...Synchronous Serial Port SSI 14 10 Am186 CC CH CU Microcontrollers User s Manual...
Страница 264: ...High Level Data Link Control HDLC 15 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 332: ...Universal Serial Bus USB 18 34 Am186 CC CH CU Microcontrollers User s Manual...
Страница 348: ...Register Summary A 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 376: ...Index Index 18 Am186 CC CH CU Microcontrollers User s Manual...