The MSM6636B is a transmission controller for automotive LAN based on data communication protocol SAE-J1850. This device can realize a data bus topology bus LAN system with a PWM bit encoding method (41.6 kbps). In addition to a protocol control circuit, MSM6636B has an enclosed quartz oscillation circuit, host CPU interface (parallel interface), a transmit/receive buffer, and a bus receiver circuit that decreases the burden on the host CPU.