App note from STMicroelectronics on possible alternate switching of channels to cater multiple communication routes. Link here (PDF)
Application engineers often face the problem of limited number of serial communication peripherals of a microcontroller that, on the other hand fulfills all the other application requirements thanks to its features and performance. Sometimes they obviate by switching to a higher level microcontroller with sufficient number of communication peripherals. This migration brings with it additional (often unused) performance and functionality, in most cases unneeded and not used by application, in addition to increased costs and PCB complexity.
A frequent case is when full (or specific) functionality is not required for each and every channel, in this case the communication flow and its control can be simplified radically (e.g. communication is required at specific modes or time slots only, communication speed can be lower, correct timing is not strictly required for all the signals, simplified protocol or flow is acceptable). In these specific cases the user would really benefit from methods on how to supplement the missing channel(s) with current HW, to avoid needless migrations.