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ST63T69B1 数据表(PDF) 11 Page - STMicroelectronics |
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ST63T69B1 数据表(HTML) 11 Page - STMicroelectronics |
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11 / 71 page  ST6369 CORE (Continued) Indirect Registers (X, Y). These two indirect reg- isters are used as pointers to the memory locations in the data space. They are used in the register-in- direct addressing mode.These registers can be addressed in the data space as RAM locations at the 80H (X) and 81H (Y) addresses. They can also be accessed with the direct, short direct, or bit di- rect addressing modes. Accordingly, the ST638x instruction set can use the indirect registers as any other register of the data space. Short Direct Registers (V, W). These two regis- ters are used to save one byte in short direct ad- dressing mode. These registers can be addressed in the data space as RAM locations at the 82H (V) and 83H (W) addresses. They can also be ac- cessed with the direct and bit direct addressing modes. Accordingly, the ST638x instruction set can use the short direct registers as any other reg- ister of the data space. Program Counter (PC) The program counter is a 12-bit register that con- tains the address of the next ROM location to be processed by the core. This ROM location may be an opcode, an operand, or an address of operand. The 12-bit length allows the direct addressing of 4096 bytes in the program space. Nevertheless, if the program space contains more than 4096 loca- tions, the further program space can be addressed by using the Program ROM Page Register. The PC value is incremented, after it is read for the address of the current instruction, by sending it through the ALU, so giving the address of the next byte in the program. To execute relative jumps the PC and the offset values are shifted through the ALU, where they will be added, and the result is shifted back into the PC. The program counter can be changed in the following ways: JP (Jump) instruction.... PC= Jump address CALL instruction ........... PC=Call address Relative Branch instructions ................... PC=PC+offset Interrupt........................ PC=Interrupt vector Reset ............................ PC=Reset vector RET & RETI instructions............ PC=Pop (stack) Normal instruction ........ PC= PC+1 WHEN CALL OR INTERRUPT REQUEST OCCURS STACK LEVEL 1 STACK LEVEL 2 STACK LEVEL 3 STACK LEVEL 4 STACK LEVEL 5 STACK LEVEL 6 PROGRAM COUNTER WHEN RET OR RETI OCCURS VA000424 Figure 5. Stack Operation Flags (C, Z) The ST6369 Core includes three pairs of flags that correspond to 3 different modes: normal mode, in- terrupt mode and Non-Maskable-Interrupt-Mode. Each pair consists of a CARRY flag and a ZERO flag. One pair (CN, ZN) is used during normal op- eration, one pair is used during the interrupt mode (CI,ZI) and one is used during the not-maskable in- terrupt mode (CNMI, ZNMI). The ST6369 Core uses the pair of flags that corre- sponds to the actual mode: as soon as an interrupt (resp. a Non-Maskable-Interrupt) is generated, the ST6369 Core uses the interrupt flags (resp. the NMI flags) instead of the normal flags. When the RETI in- struction is executed, the normal flags (resp. the in- terrupt flags) are restored if the MCU was in the normal mode (resp. in the interrupt mode) before the interrupt. Should be observed that each flag set can only be addressed in its own routine (Not-maskable interrupt, normal interrupt or main routine). The inter- rupt flags are not cleared during the context switch- ing and so, they remain in the state they were at the exit of the last routine switching. The Carry flag is set when a carry or a borrow oc- curs during arithmetic operations, otherwise it is cleared. The Carry flag is also set to the value of the bit tested in a bit test instruction, and partici- pates in the rotate left instruction. The Zero flag is set if the result of the last arithmetic or logical operation was equal to zero, otherwise it is cleared. The switching between these three sets is auto- matically performed when an NMI, an interrupt and a RETI instructions occur. As the NMI mode is automatically selected after the reset of the MCU, the ST6369 Core uses at first the NMI flags. ® ST6369 7/67 |
类似零件编号 - ST63T69B1 |
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类似说明 - ST63T69B1 |
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