OBD-ii UART adapter, with multiple protocols active

Hello,

Project is a device that reads from one CANBUS protocol (J1939), interprets messages and converts to a different CANBUS protocol (J1850). The device will need to read from both, and might need to send messages on both buses too.

I’m wondering if I’ll need to buy 2 of the OBD2-UART devices, or if a single device is capable of being active on both interfaces at the same time. The documentation doesn’t have a AT command that jumps out at me as how you would specify which interface a given message goes to. If there is a way to change the active interface, how long does it take to ‘activate’?

Thanks in advance!