The supermonitor does two simple things to read the codes. First it grounds TE which causes the ECU to go into diagnostic mode and flash the 'check engine light'. Second, it counts the pulses on the CEL and converts them to the diagnostic number.
The ECU can output the diagnostic data you seek, but it takes some real work to get at it. The reference is posted above but there is no magic cable you can buy to get to it , at least for now.