Microcomputer Circuits and Processes

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Second EXECUTE cycle MOV M--+Acc, clock period 1 The instruction 'Move the contents of memory into the accumulator' has been fetched into the instruction register. This has code 0110. Now this instruction must be executed. Remember that the address from where the data must be read is held by register A. So this address must first be loaded into the address latch. To do this, the instruction decoder enables register Ns buffer, thus putting the address DIllon to the bus. The instruction decoder also sends out an ALE signal which loads this new address into the address latch. Memory location 0111 is thus Figure 3.18 addressed. CPU MEM 001 0 o 1 1 1 o 1 1 0 1 1 1 1 o 1 0 1 o 1 1 1 o 0 0 0 o 1 1 0 Second EXECUTE cycle MOV M--+Acc, clock periods 2 and 3 Here, in two clock periods, the contents of memory location 0111, which is the number 0110 (6 10 ), is moved· into the accumulator. The instruction decoder sends a read (RD) signal to memory putting the number 0110 on to the bus, and then it enables the accumulator's buffer, allowing the number 0110 to pass into the accumulator. This is the end of the second EXECUTE cycle, which has loaded 0110 into the Figure 3.19 accumulator, as directed by register A. CPU MEM o o 38
Third EXECUTE cycle AD I, clock period 1 The instruction which has now been fetched into the instruction decoder has code 1111. This is an ADD IMMEDIATE (ADI) instruction. Note how the program counter has been incremented, as usual, during a FETCH, and now holds number 0100. Now the program counter is enabled on to the bus, by the instruction decoder, which also sends out an ALE signal to enter the contents of the program counter, 0100, into the address latch. The immediate number (after the ADI instruction), 0101, which lives at address 0100, is now addressed, ready Figure 3.20 for the addition. CPU MEM o o Third EXECUTE cycle ADI, clock period 2 Since this instruction is an 'immediate' type, the program counter must be incremented to skip over the data number 0101, ready for the next Figure 3.21 instruction. CPU MEM 39
Page 2 and 3: General editor. Revised Nuffield Ad
Page 4 and 5: Longman Group Limited Longman House
Page 6 and 7: PROLOGUE This Reader explains how m
Page 8 and 9: transistor, through the logic circu
Page 10 and 11: tasks (large computing 'power'), wa
Page 12 and 13: 800000 mark. Such high sales result
Page 14 and 15: CHAPTER 2 THE ELECTRONICS MICROCOMP
Page 16 and 17: enabled, as the truth table in figu
Page 18 and 19: D memory cell storing binary 0 stor
Page 20 and 21: address bus r----- AND gates RD .--
Page 22 and 23: If you get the chance, look up 7415
Page 24 and 25: Period 2 Period 3 The data bits are
Page 26 and 27: transfers the full 16 bits of addre
Page 28 and 29: INPUT AND OUTPUT Devices that input
Page 30 and 31: A glance at the timing diagram in f
Page 32 and 33: CHAPTER 3 RUNNING A SIMPLE PROGRAM
Page 34 and 35: adding is represented by 1111. Figu
Page 36 and 37: The number moved into register A im
Page 38 and 39: loaded into register A. So the CPU
Page 40 and 41: The FETCH cycles FETCH cycles, whic
Page 42 and 43: The EXECUTE cycles During EXECUTE c
Page 46 and 47: Third EXECUTE cycle ADI, clock peri
Page 48 and 49: That is the end of the program, exc
Page 50 and 51: CHAPTER 4 MEMORIES, INTERFACES, AND
Page 52 and 53: measurements made from a microproce
Page 54 and 55: (al (bl Figure 4.6 (a) Same as in f
Page 56 and 57: A typical bubble unit contains 300
Page 58 and 59: (al driver displays 0 1 1 0 1 0 0 1
Page 60 and 61: Where exactly is this common line c
Page 62 and 63: this R is in series with the next h
Page 64 and 65: That is the principle of the conver
Page 66 and 67: comparator digital-to-analogue data
Page 68 and 69: II CI l! ~L--~---- desired measurem
Page 70 and 71: except that it is sent out bit afte
Page 72 and 73: These equally spaced voltages are f
Page 74 and 75: Figure 4.35 shows how the letter 'D
Page 76 and 77: A CONTROL AND DATA AQUISITION COMPU
Page 78 and 79: It does this by outputting a signal
Page 80 and 81: The second application, shown in fi
Page 82 and 83: INDEX This Index will direct you to

Microcomputer Circuits and Processes

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