Serial Bus Thruput Doubling by Using Variable Pulse Width Modulation

The 10.4 kbit/s SAE J-1850 serial data link specifies Variable Pulse Width Modulation (VPWM)* encoding for its single wire system. This paper begins with a description of serial data link requirements in an automotive environment, and then discusses two key areas which lead to the use of VPWM and its implementation. A comparison of encoding approaches and their relative merits and weak points arrives at the use of VPWM for single wire low radiated emissions arbitrated busses. The second key area of implementation is covered in a discussion of timing and synchronization approaches with emphasis on system integrity in a characteristically noisy environment.