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
Summary of Contents for Am186 CC
Page 1: ...Am186 CC CH CU Microcontrollers User s Manual Order 21914B...
Page 4: ...iv Am186 CC CH CU Microcontrollers User s Manual...
Page 18: ...Table of Contents xviii Am186 CC CH CU Microcontrollers User s Manual...
Page 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
Page 40: ...Architectural Overview 1 16 Am186 CC CH CU Microcontrollers User s Manual...
Page 86: ...System Overview 3 36 Am186 CC CH CU Microcontrollers User s Manual...
Page 92: ...Emulator Support 4 6 Am186 CC CH CU Microcontrollers User s Manual...
Page 112: ...DRAM Controller 6 8 Am186 CC CH CU Microcontrollers User s Manual...
Page 134: ...Interrupts 7 22 Am186 CC CH CU Microcontrollers User s Manual...
Page 186: ...Programmable I O Signals 9 8 Am186 CC CH CU Microcontrollers User s Manual...
Page 200: ...Watchdog Timer 11 6 Am186 CC CH CU Microcontrollers User s Manual...
Page 232: ...Asynchronous Serial Ports UARTs 13 24 Am186 CC CH CU Microcontrollers User s Manual...
Page 242: ...Synchronous Serial Port SSI 14 10 Am186 CC CH CU Microcontrollers User s Manual...
Page 264: ...High Level Data Link Control HDLC 15 22 Am186 CC CH CU Microcontrollers User s Manual...
Page 332: ...Universal Serial Bus USB 18 34 Am186 CC CH CU Microcontrollers User s Manual...
Page 348: ...Register Summary A 16 Am186 CC CH CU Microcontrollers User s Manual...
Page 376: ...Index Index 18 Am186 CC CH CU Microcontrollers User s Manual...