[MetroMPG]

More SW smartness:

That site also has an example using the chip for which they're selling the firmware & tools that implements a 4-channel A/D voltage logger. That chip is actually an 8-bit microprocessor with the A/D, and a small amount of program memory built in. It may even have voltage conversion buffers required to convert serial communication to true RS232 (I'm not sure).

In contrast, the 8051 is the chip used in many ECUs (like Honda) and is powerful enough to be useful independent of a PC. It's a faster 8-bit microprocessor, with 4 built-in 8-bit I/O ports but no built-in A/D chip. For that, you'd probably use something like the ADC0838. Serial I/O would be optional but you'd probably want to use one in order to program/debug/data-dump the thing.