Change value at specific address in assembly

Question

I'm writing assembly in LC-3. I have a register, R1, that points to a specific address. How do I change the value at that address to 0? Unfortunately, this is due really soon, so prompt help would be greatly appreciated! Thanks!

PS: If you don't know LC-3, here are the 15 instructions: ADD, AND, BR, JMP, JSR, JSRR, LD, LDI, LDR, LEA, NOT, RET, RTI, ST, STI, STR, TRAP

Answer 1

You'd start by zeroing another register (e.g., R0). Since there's no instruction to clear a register, one obvious choice would to AND that register with an immediate value of 0 (another would be to subtract the register from itself). Likewise, the instruction set doesn't have a simple "store indirect", but it does have a "store indirect with offset" (STR), so your source register would be the one you cleared, the destination register would be R1, and the offset would be 0 (#0).