3 ms·
In chips because of the layers of conductors and insulators you are actually charging a capacitor, not just sending a signal down a lone wire.
by krupan 5y ago
In chips because of the layers of conductors and insulators you are actually charging a capacitor, not just sending a signal down a lone wire.
- AshamedCaptain 5y agoThat's how all conductors work, not just "in chips due to layers of conductors and insulators". The thing is that in most situations you just model the conductor away as a "perfect ideal wire" and everything usually just works since you don't care about these small delays and/or you have very high power. But when you enter sub-nanosecond and/or sub-mW territory...
- jhgb 5y agoBut IC interconnects have a very small cross section, so for them this problem is much more pressing.
- tom-thistime 5y agoYou're always driving a waveguide that has inductance and capacitance per unit length. But when resistance is high enough you are just charging a big distributed capacitor. It's a different regime from the high-conductivity situation (which looks like a transmission line). Either picture could apply at sub-ns speeds, it depends mainly on the resistance.
- kens 5y agoYes, a long bus is like a resistor-capacitor delay circuit. You can speed it up by using a bigger driver for more current, but that takes up more space and adds its own delay. I expect that the bus in the Xbox is split in two, with a second driver in the middle. This makes the first half faster, but the second half of the bus probably takes another clock cycle, which would explain the observed behavior.