4 ms·
Since the 386 is a 32-bit processor, the address specifies a 32-bit word and doesn't use address bits A0 and A1. But what if you just want to read a byte or a 1
by kens 1y ago
Since the 386 is a 32-bit processor, the address specifies a 32-bit word and doesn't use address bits A0 and A1. But what if you just want to read a byte or a 16-bit word? The trick is that the 386 provides four Byte Enable outputs (BE0#-BE3#) that indicate which bytes in the word are being transferred. Of course, it's not that simple. If the lower 16 bits of the data bus aren't being used, the upper 16 bits of the data bus are duplicated on the lower 16 bits to make 16-bit buses more efficient (somehow).
- mrlonglong 1y agoNeat, saves two wires.
- phire 1y agoYes and no. You replaced two address pins with four byte enable pins. But the byte enable pins also implicitly communicate size, which would otherwise require another two pins. So this byte enable scheme breaks even (at least for chips with 16bit or 32bit buses). The main goal is simplify the design of the motherboard.