[longassname]

Hello Daniel,

The signaling levels used by the serial port of the ECU's processor are not ttl. The 74hc125 is designed to communicate with the same signaling levels as the processor in the ECU. It's the correct/matching driver for our ECU if you will. I use texas instruments chips sn74hc125n.

The diodes form what is called a clipping circuit. A diode tied to vcc clips the top of the signal at the vcc level. Vcc is the +5v from the ttl232r cable. A diode tied to Vss clips the signal to the Vss level. The output to the ECU is clipped on both sides. The input from the ecu is clipped low and pulled high. The solid back arrow heads (not the ones that are part of the diode symbol) are the symbol for a connection to Vcc. The arrow heads made of lines are the symbol for a connection to Vss.

In the diagram there are 2 gates (gates a and b) of 1 74hc125 chip (component U1).