352 Chapter Fourteen
Figure 14-6
Waveform Display
after the Reset
Sequence Has
Completed.
addregis loaded with the data bus value so that the 0000 value can be
used to drive the addrbus. At state reset5, the data bus is driven with
the instruction data from component memat address 0. This data is then
loaded into register instrregin reset6so that the control entity can use
the instruction contents.
The next state after reset6is the first execution step of the instruction
that was just fetched from the memory. Looking back at the description
of the mementity, we can see that the first instruction loads register 1 with
the source address of the copy operation. Figure 14-6 shows the waveform
display after the reset sequence has completed and the first instruction
has started to execute.
This instruction is a LoadI(Load Immediate) instruction that uses two
words of the memory. The instruction is shown here:LoadI 1, #
10The first word of the instruction specifies the behavior of the instruction,
and the second specifies the data to be loaded into the register specified
by the instruction. This instruction first puts the program counter value
to the data bus so that the value can be incremented. The program
counter is then able to read the second word of the instruction that contains
the data to be loaded into reg 1.
During state execute, the program counter is incremented and the
incremented value can be found as the output of the ALU aluout. During
states loadi2,loadi3, and loadi4, this value is transferred to register
addregand data is read from mementity in state loadi5. During state
loadi6, data from memory is loaded into register 1.