Controlling the a-bit

[ninmurai]

I'm trying to figure out how to control the a-bit which governs the mnemonics. Looking at Figure 4.3, it implies that a=0 when there is no "A" in the comp mnemonic.

However, I'm after the mnemonic which gives cccccc = 111111 when a=0. It's blank in that figure and when I use the instruction "AMD=1;JMP", it gives 1110 1111 1111 1111, presumably because I'm forcing the a=0 mnemonic because of the "1" comp instruction.

What can I do here?

[cadet1620]

The "a" bit in the c-instruction says to read or write to RAM instead of the A register.

The easiest way to deal with it is to consider it as the most significant bit of a 7-bit compute field. Include all the legal computations in a lookup table that returns the seven bits acccccc and merge them as a single element into the opcode that you are generating.

--Mark