Question

Assume we have CPU instructions that look like this:

load register, address

save register, address

Where the instruction load copies the data pointed to by the address into the register, and the instruction save copies the data from the register into the location pointed to by address. Assume “register” can be the values R0 and R1, where each “R#” is the name of a single register that can store a single byte.

Assume the “address” is an integer constant number. Assume at address 52 is the beginning of a string “ABC”. Assume at address 1 is the printer.

Using only the above two instructions, write code that sends each byte of the string to the printer.

Answer 1

So we need to just use the above two commands in order to store the "ABC" to the printer. So we need to go to each character one by one. As it is starting at 52 so next one would be 53 and then would be 54

LOAD R1, 0x34
STORE R1, 0x01
LOAD R1, 0x35
STORE R1, 0x01
LOAD R1, 0x36
STORE R1, 0x01

So the first line will load the character 'A' of one byte to Register R1, then it is stored to the printer and then 'B' loaded to Register R2 and then 'C' loaded to Printer using Register R1 only.

Thus in this way, three bytes of 'ABC' are written to the printer.

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