retrolefty the diagram I posted on the first page is basically the same thing you posted just it's not a one chip package. It's from TI appnote.
The this is not that hard of a deal 4 mA is the low 20 is the high you can send t data stream out like that that's easy to read. This was used back before rs232 to send data the first IBM pc had 4 to 20 on the card that had the com port on it and people rented phone lines to send data over the copper wire this way.
MIDI is a digital forum of this