Below is a Little Man program that solves exercise 6.9, p. 164, from textbook. The program is very similar to the LMC program which you will find in the lecture notes on Chapter 6 posted on Blackboard and discussed in Panopto. The difference is that the program below is somewhat simpler as it uses only 2 branches (BRZ 09 and BR 01), whereas the program in the lecture notes uses 3 branches (BRP 05, BR 10, and BR 01). First, try to understand each instruction thoroughly and then trace the execution of each instruction. Address Instruction (Mnemonics) 03 IN 04 STO 18 05 BRZ 12 06 IN 07 ADD 20 08 STO 20 09 LDA 18 10 SUB 16 11 BR 04 12 LDA 20 13 OUT 14 HLT Address Contents 18 DAT ? 2 1 0 (decremented by 1 each time the loop is executed) 19 DAT 1 20 DAT 0 Assume now that the above program will only read 3 numbers. That is, the following numbers in this order will be placed, one at a time, in the In-basket: 2, 18, and 15, where 2 is the count of numbers that follow, and 18 and 15 are the numbers that are to be added. The first column in the table on page 3 shows the order in which the instructions from the program will be executed. Trace the execution of these instructions and determine the contents of the PC before and after each instruction is executed. Also, write down in the table the contents of the In-basket; Accumulator; Memory locations 18, 19, and 20; and Out-basket after each instruction is executed. Memory location 18 controls the loop. It initially contains an unknown value (?), then 2, next 1, and finally 0. Memory location 19 always contains 1. It is used to decrease the loop count by 1. Memory location 20 is initialized with 0, and finally it stores 33, the sum of 18 and 15. The entry 03 04 in the PC column means that the PC is 03 when the instruction IN started and is changed to 04 when the instruction IN is finished.

The sequence in which instructions are executed	PC before after	In-basket	Accumulator	Memory location 18	Memory location 19	Memory location 20	Out-basket
IN	03 04	2	2	?	1	0	?
STO 18
BRZ 12
IN
ADD 20
STO 20
LDA 18
SUB 19
BR 04
STO 18
BRZ 12
IN
ADD 20
STO 20
LDA 18
SUB 19
BR 04
STO 18
BRZ 12
LDA 20
OUT
HLT