Loading Jump Time

Hello everyone! I lost track of time, and it appears I have once more logged too many hours with no devlog, yet no excuses I have. Let’s get right to it!

HL and D8

A lot of Instructions that I had already made have an HL target, in which they use the value in the joint register HL as an address in memory, and perform the operation on that byte. Up until this point, all HL targets were todos, but, since I had created the memory bus, I was able to quickly wire up those targets. A lot of those same instructions could also take the next byte in memory as the input (D8) so I wired those up too (though before HL). I actually wasn’t sure whether HL targets used a different memory bus than the one used for operations.

JP Morgan

The next instruction to deal with was JP (jump). Based on different conditions (the state of the zero flag or carry flag, or always) it would or wouldn’t jump to the address encoded over the next two bytes. Probably one of the easier instructions I’ve made.

Loading…

After JP was load. LD just copies data from one place to another. There are so many variations that I can’t talk about all of them, and there my code is too long for this devlog, so:

Byte: Load a byte from point a to point b
Word: just like the Byte type except with 16-bit valuesAFromIndirect: load the A register with the contents from a value from a memory location whose address is stored in some locationIndirectFromA: load a memory location whose address is stored in some location with the contents of the A registerAFromByteAddress: Just like AFromIndirect except the memory address is some address in the very last byte of memory.ByteAddressFromA: Just like IndirectFromA except the memory address is some address in the very last byte of memory.

This is the opcode table I’ve been using