The MSM6636 is a transmission controller for automotive LAN based on data communication protocol SAE-J1850. This LSI can realize a data bus topology bus LAN system with a PWM bit encoding method (41.6 K bps). In addition to a protocol control circuit, MSM6636 has an enclosed quartz oscillation circuit, host CPU interface (clock synchronous serial / UART), a transmit/ receive buffer, and a bus receiver circuit that decreases the burden on the host CPU.