Chapter 2 Organization of Computers 2.1.2 Instruction Cycle may require a different sequence of operations to execute the on Next, the microprocessor decodes the instruction. Each instructi instruction. When the microprocessor decodes the instruction, it determines which instruction it is in order to select the correct sequence of operations to perform. This is done entirely within the microprocessor; it does not use the system buses 接下来,微处理器对这条指令译码。每一条指令可能要有不同 的操作序列来执行。当微处理器对该指令译码是,它确定处理 的是哪一条指令以便选择正确的操作序列去执行。这一步完全 在微处理器内完成,不需要使用系统总线。 计算机专业英语
Chapter 2 Organization of Computers 计算机专业英语 2-16 Next, the microprocessor decodes the instruction. Each instruction may require a different sequence of operations to execute the instruction. When the microprocessor decodes the instruction, it determines which instruction it is in order to select the correct sequence of operations to perform. This is done entirely within the microprocessor; it does not use the system buses. 接下来，微处理器对这条指令译码。每一条指令可能要有不同 的操作序列来执行。当微处理器对该指令译码是，它确定处理 的是哪一条指令以便选择正确的操作序列去执行。这一步完全 在微处理器内完成，不需要使用系统总线。 2.1.2 Instruction Cycle
Chapter 2 Organization of Computers 2.1.2 Instruction Cycle Finally, the microprocessor executes the instruction. The sequence of operations to execute the instruction varies from instruction to instruction The execute routine may read data from memory, write data to memory, read data from or write data to an lO device, perform only operations within the CPU, or perform some combination of these operations. We now look at how the computer performs these operations from a system perspective 最后,微处理器执行该指令。指令不同,执行的操作序列也不 同。执行过程可以是从存储器读取数据,写数据到存储器,读 或写数据到ⅣO设备,执行CPU内部操作或者执行多个上述操作 的组合。下面我们从系统的角度来看计算机是怎样执行这些操 作的。 计算机专业英语 2-17
Chapter 2 Organization of Computers 计算机专业英语 2-17 Finally, the microprocessor executes the instruction. The sequence of operations to execute the instruction varies from instruction to instruction. The execute routine may read data from memory, write data to memory, read data from or write data to an I/O device, perform only operations within the CPU, or perform some combination of these operations. We now look at how the computer performs these operations from a system perspective. 最后，微处理器执行该指令。指令不同，执行的操作序列也不 同。执行过程可以是从存储器读取数据，写数据到存储器，读 或写数据到I/O设备，执行CPU内部操作或者执行多个上述操作 的组合。下面我们从系统的角度来看计算机是怎样执行这些操 作的。 2.1.2 Instruction Cycle
Chapter 2 Organization of Computers 2.1.2 Instruction Cycle To read data from memory, the microprocessor performs the same sequence of operations it uses to fetch an instruction from memory After all, fetching an instruction is simply reading it from memory Figure 2-2(a) shows the timing of the operations to read data from memory 微处理器从存储器读取数据所执行的操作序列,同从存储器中 去一条指令是一样的。毕竞取指令就是简单地从存储器中读取 它。图2-2(a)显示了从存储器中读取数据的操作时序。 计算机专业英语 2-18
Chapter 2 Organization of Computers 计算机专业英语 2-18 To read data from memory, the microprocessor performs the same sequence of operations it uses to fetch an instruction from memory. After all, fetching an instruction is simply reading it from memory. Figure 2-2(a) shows the timing of the operations to read data from memory. 微处理器从存储器读取数据所执行的操作序列，同从存储器中 去一条指令是一样的。毕竟取指令就是简单地从存储器中读取 它。图2-2(a)显示了从存储器中读取数据的操作时序。 2.1.2 Instruction Cycle
Chapter 2 Organization of Computers 2.1.2 Instruction Cycle In Figure 2-2, notice the top symbol, CLK. This is the computer system clock; the microprocessor uses the system clock to synchronize its operations. The microprocessor places the address onto the bus at the beginning of a clock cycle, a 0/1 sequence of the system clock. One clock cycle later, to allow time for memory to decode the address and access its data, the microprocessor asserts the read Signal. This causes memory to place its data onto the system data bus. During this clock cycle, the microprocessor reads the data off the system bus and stores it in one of its registers. At the end of the clock cycle it removes the address from the address bus and deasserts the read signal memory then removes the data from the data bus, completing the memory read operation 在图2-2中,注意最上面的符号CLK,它是计算机的系统时钟,微处理器用系统时钟 使其操作同步。在一个时钟周期(系统时钟的01序列)的开始位置,微处理器将地 址放到总线上。一个时钟周期(允许存储器对地址译码和访问数据的时间)之后 微处理器才发出读信号。这使得存储器将数据放到数据总线上。在这个时钟周期之 内,微处理器从系统总线上读取数据,并存储到它的某个寄存器中。在这个时钟周 期结束时,微处理器撤消地址总线上的地址,并撤消读信号。然后存储器从数据总 线上撒消数据,也就完成了存储器的读操作 2-19
Chapter 2 Organization of Computers 计算机专业英语 2-19 In Figure 2-2, notice the top symbol, CLK. This is the computer system clock; the microprocessor uses the system clock to synchronize its operations. The microprocessor places the address onto the bus at the beginning of a clock cycle, a 0/1 sequence of the system clock. One clock cycle later, to allow time for memory to decode the address and access its data, the microprocessor asserts the READ Signal. This causes memory to place its data onto the system data bus. During this clock cycle, the microprocessor reads the data off the system bus and stores it in one of its registers. At the end of the clock cycle it removes the address from the address bus and deasserts the READ signal. Memory then removes the data from the data bus, completing the memory read operation. 在图2-2中，注意最上面的符号CLK，它是计算机的系统时钟，微处理器用系统时钟 使其操作同步。在一个时钟周期（系统时钟的0/1序列）的开始位置，微处理器将地 址放到总线上。一个时钟周期（允许存储器对地址译码和访问数据的时间）之后， 微处理器才发出读信号。这使得存储器将数据放到数据总线上。在这个时钟周期之 内，微处理器从系统总线上读取数据，并存储到它的某个寄存器中。在这个时钟周 期结束时，微处理器撤消地址总线上的地址，并撤消读信号。然后存储器从数据总 线上撤消数据，也就完成了存储器的读操作。 2.1.2 Instruction Cycle
Chapter 2 Organization of Computers 2.1.2 Instruction Cycle The timing of the memory write operation is shown in Figure 2-2(b).The processor places the address and data onto the system buses during the first clock cycle. The microprocessor then asserts a WRITE control signal (or its equivalent) at the start of the second clock cycle. Just as the READ signal causes memory to read data, the WRItE signal triggers memory to store data. Some time during this cycle, memory writes the data on the data bus to the memory location whose address is on the address bus. At the end of this cycle, the processor completes the memory write operation by removing the address and data from the system buses and deasserting the WRITE signal 存储器写操作的时序如图2-2(b所示。在第一个时钟周期,处理器将地址和 数据放到总线上,然后在第二个时钟周期开始时发出一个写(WRIE)控 制信号(或与之等价的信号)。像读信号促使存储器读取数据一样,写信号 促使存储器存储数据。在这个时钟周期的某个时刻,存储器将数据总线上的 数据写入地址总线指示的存储单元内。当这个时钟周期结束,微处理器从系 统总线上撤消地址、数据及写信号后,就完成了存储器的写操作。 2-20
Chapter 2 Organization of Computers 计算机专业英语 2-20 The timing of the memory write operation is shown in Figure 2-2(b). The processor places the address and data onto the system buses during the first clock cycle. The microprocessor then asserts a WRITE control signal (or its equivalent) at the start of the second clock cycle. Just as the READ signal causes memory to read data, the WRITE signal triggers memory to store data. Some time during this cycle, memory writes the data on the data bus to the memory location whose address is on the address bus. At the end of this cycle, the processor completes the memory write operation by removing the address and data from the system buses and deasserting the WRITE signal. 存储器写操作的时序如图2-2(b)所示。在第一个时钟周期，处理器将地址和 数据放到总线上，然后在第二个时钟周期开始时发出一个写（WRITE）控 制信号（或与之等价的信号）。像读信号促使存储器读取数据一样，写信号 促使存储器存储数据。在这个时钟周期的某个时刻，存储器将数据总线上的 数据写入地址总线指示的存储单元内。当这个时钟周期结束，微处理器从系 统总线上撤消地址、数据及写信号后，就完成了存储器的写操作。 2.1.2 Instruction Cycle