Little Man Computer Task 1 Last lesson you were asked to write a program to multiply two numbers together. The next slide has a working program to do this. You will need to adapt this program this lesson to perform a different task.

Program to multiply 2 numbers 500-Input x 291-Store acc. as x 500-Input y 292-Store acc. as y 193-Load z in to acc. 391-Add x to acc. value 293-Store acc. as z 192-Load y in to acc. 499-Minus one from acc. 292-Store acc. as y 801-Skip next if acc. is zero 905-Jump to instruction Load z in to acc. 600-Output acc. 700-Halt 1xx Load 2xxStore 3xx Add 4xx Subtract 500 Input 600 Output 700 Halt 800 Skip If Negative 801 Skip If Zero 802 Skip If Positive 9xx Jump

Little Man Computer Task 2 Write a program to divide two numbers. Write the program in word, or on paper, before using the LMC program. The program should output the quotient, and then the remainder. e.g. for the calculation 10/3 the program would output 3 and 1. If you finish the program this lesson, use the LMC program and the ‘Registers’ Slide, to help you answer the exam question on the last slide of this file.

The addition method take the divisor and add it to itself. update a counter. Check if it equals the number that is being divided. If not, do the same addition, and update your counter again. keep going till you see that the sum is equal to or greater than the number that is to be divided. Then the value of your counter is the quotient. To get the remainder, (divisor - (final sum - divident)) for example. take 10/ = 6 counter = = 9 counter = = 12 counter = 3 (now 12 > 10 hence quotient = counter = 3) remainder = 3 - ( ) = 1

The addition method take 22/ = 10 counter = = 15 counter = = 20 counter = = 25 counter = 4 (now 25 > 22 hence quotient = counter = 4) remainder = 5 - ( ) = 2

The subtraction method take the divident and subtract the divisor from it. update a counter. Check if it equals the number that is being divided. If not, do the same addition, and update your counter again. keep going till you see that the sum is equal to or greater than the number that is to be divided. Then the value of your counter is the quotient. To get the remainder, (divisor - (final sum - divident)) for example. take 10/ = 7 counter = = 4 counter = = 1 counter = 3 (now 1 < 3 hence quotient = counter = 3) remainder = final value = 1

The subtraction method take 22/ = 17 counter = = 12 counter = = 7 counter = = 2 counter = 4 (now 4 < 5 hence quotient = counter = 4) remainder = final value = 2

LMC Instruction Set 1LoadReverse of Store: walks to the mbox specified, copies the instruction on the slip of paper and takes it to the calculator and punches the number in. 2Storewalk to calculator, reads the number there, and writes the number on a slip of paper, walks to the mbox specified in the instruction, and puts this slip of paper there (replacing any paper already there

LMC Instruction Set 3Addwalk to mailbox address specified and read the number there; walk to calculator and adds it to the number already in the calculator 4Subtractsimilar to add but subtracts 5Inputwalks to the in box and picks up the slip of paper having a 3-digit number on it; walks over to the calculator and enters that number

LMS Instruction Set 6Outputwalk to calculator, reads the number there, and writes the number on a slip of paper, walks to the out box and puts this slip of paper there 7Haltstop 800Skip if Negative walk to calculator; if the value is less than zero then walk to prog. counter and add one to the current value

LMS Instruction Set 801Skip If Zerowalk to calculator; if the value is zero then walk to prog. counter and add one to the current value 802Skip If Positive walk to calculator; if the value is greater than zero then walk to prog. counter and add one to the current value 9JumpTells LMC to change the program counter to the number shown on the address portion

Registers Different CPU designs have different numbers and types of registers. The following four types of registers, however, are found in all designs: PC, the program counter. The PC tells the CPU which memory location contains the next instruction to be executed. Typically, the PC is incremented by 1 so that it points to the next instruction in memory. But branch instructions can set the PC to another value. – In the LMC, the "program counter" is represented as the Location Counter. IR, the instruction register. This register is important because it holds the instruction that is currently being executed. – In the LMC, the "instruction register" is shown as the Instruction Display. To visualize the LMC operation, we can picture the Little Man holding the instruction written on a slip of paper he has taken from a mailbox, and reading what needs to be done. MAR, the memory address register. This register tells the CPU which location in memory is to be accessed. – The MAR is not shown in the LMC. MDR, the memory data register. This register holds the data being put into or taken out of the memory location identified by the MAR. It is sometimes called the memory buffer register, or MBR.

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