Is filling up plan cache causes a decrease in space allocated for data cache?

SQL Server uses allocated server memory for different kind of purposes. Two of them are plan cache and data cache which are used to store execution plans and actual data correspondingly.

My question: Do these two caches have different allocated space section in Buffer pool, or in contrary, they have just one section in Buffer pool which they share between each other?

In other words, if plan cache is filling up, does space for data cache is reducing as well?