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ATAR892-C Datasheet(PDF) 7 Page - ATMEL Corporation |
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ATAR892-C Datasheet(HTML) 7 Page - ATMEL Corporation |
7 / 108 page 7 4593D–4BMCU–05/06 ATAR092-C/ATAR892-C 4.2.3.6 Top of Stack (TOS) The top of stack register is the accumulator of the MARC4. All arithmetic/logic, memory refer- ence and I/O operations use this register. The TOS register receives data from the ALU, ROM, RAM or I/O bus. 4.2.3.7 Condition Code Register (CCR) The 4-bit wide condition code register contains the branch, the carry and the interrupt enable flag. These bits indicate the current state of the CPU. The CCR flags are set or reset by ALU operations. The instructions SET_BCF, TOG_BF, CCR! and DI allow direct manipulation of the condition code register. 4.2.3.8 Carry/Borrow (C) The carry/borrow flag indicates that the borrowing or carrying out of Arithmetic Logic Unit (ALU) occurred during the last arithmetic operation. During shift and rotate operations, this bit is used as a fifth bit. Boolean operations have no affect on the C-flag. 4.2.3.9 Branch (B) The branch flag controls conditional program branching. Should the branch flag have been set by a previous instruction, a conditional branch will cause a jump. This flag is affected by arith- metic, logic, shift, and rotate operations. 4.2.3.10 Interrupt Enable (I) The interrupt enable flag globally enables or disables the triggering of all interrupt routines with the exception of the non-maskable reset. After a reset or while executing the DI instruction, the interrupt enable flag is reset, thus disabling all interrupts. The core will not accept any further interrupt requests until the interrupt enable flag has been set again by either executing an EI or SLEEP instruction. 4.2.4 ALU The 4-bit ALU performs all the arithmetic, logical, shift and rotate operations with the top two ele- ments of the expression stack (TOS and TOS-1) and returns the result to the TOS. The ALU operations affect the carry/borrow and branch flag in the condition code register (CCR). Figure 4-5. ALU Zero-address Operations TOS-1 CCR RAM TOS-2 SP TOS-3 TOS ALU TOS-4 |
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