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AT90S8414
Preliminary
4-23
registers within the address range $00 - $19 are directly bit-accessible using the SBI and CBI instructions. In these
registers, the value of single bits can be checked by using the SBIS and SBIC instructions. Refer to the instruction set
chapter for more details.
The different I/O and peripherals control registers are explained in the following chapters.
THE STATUS REGISTER - SREG
The
AVR
status register - SREG - at I/O space location $3F is defined as:
Bit
7
6
5
4
3
2
1
0
$3F
I
T
H
S
V
N
Z
C
SREG
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial value
0
0
0
0
0
0
0
0
Bit 7 - I : Global Interrupt Enable:
The global interrupt enable bit must be set (one) for the interrupts to be enabled. The individual interrupt enable control is
then performed in the interrupt mask registers - GIMSK and TIMSK. If the global interrupt enable register is cleared
(zero), none of the interrupts are enabled independent of the GIMSK and TIMSK values. The I-bit is cleared by hardware
after an interrupt has occurred, and is set by the RETI instruction to enable subsequent interrupts.
Bit 6 - T : Bit Copy Storage:
The bit copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T bit as source and destination for the operated
bit. A bit from a register in the register file can be copied into T by the BST instruction, and a bit in T can be copied into
a bit in a register in the register file by the BLD instruction.
Bit 5 - H : Half Carry Flag:
The half carry flag H indicates a half carry in some arithmetic operations. See the Instruction Set Description for detailed
information.
Bit 4 - S : Sign Bit, S = N
Å
Å
V :
The S-bit is always an exclusive or between the negative flag N and the two’s complement overflow flag V. See the
Instruction Set Description for detailed information.
Bit 3 - V : Two’s Complement Overflow Flag:
The two’s complement overflow flag V supports two’s complement arithmetics. See the Instruction Set Description for
detailed information.
Bit 2 - N : Negative Flag:
The negative flag N indicates a negative result after the different arithmetic and logic operations. See the Instruction Set
Description for detailed information.
Bit 1 - Z : Zero Flag:
The zero flag Z indicates a zero result after the different arithmetic and logic operations. See the Instruction Set
Description for detailed information.
Bit 0 - C : Carry Flag:
The carry flag C indicates a carry in an arithmetic or logic operation. See the Instruction Set Description for detailed
information.
Содержание AT90S8414
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