Talk:Control store

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The control store usually has on its outputs a register. It must be obvious that the outputs that go back into the sequencer to determine the next address have to go through some sort of register to prevent a race condition being created. However it turns out that in most designs it pays for all of the other bits to also go through a register. This is because the machine will work faster if the execution of the next microinstruction is delayed by one cycle. This register is known as a pipeline register. The point is that very often the execution of the next microinstruction is dependent on result of the current microinstruction that will not be stable till the end of the current microcycle. It can be seen that either way all of the outputs of the control store go into one big register. In the olden days it used to be possible to buy EPROMS with these register bits on the same chip.

I'm not at all happy with this paragraph. First of all even I am confused what the author is getting at. Please expound on what is meant with race condition, i.e. when there is more than one sequencer at work here etc. The predictive branching aspect is pretty interesting here too but I think we should keep the concepts presented here a little simpler...

Hell, do you know those wind up music toys with a metal drum with spikes on it...? The spikes on the metal drum.. that's the microcode (and the drum is the control storage). As the drum rotates the spikes cause the metal tabs to vibrate producing the melody..

That's a nice introduction to the concepts here and then we can move on and tell people what a microsequencer is and then go all the way and provide a sample microcode for an extremely simplified CPU. 84.160.239.19 23:19, 17 January 2006 (UTC)

[edit] Diode rom?

The article says: "Modern VLSI CPUs also use a diode matrix for the read-only control store."

I would be surprised, if for example the pentium4 processor has a diode matrix in it. Maybe someone who knows more about such things kan change the article if the newest processors indeed don't have diode matrixes.