typedef struct Ringbuffer {
  uint8_t wrIdx;
  uint8_t lag;
  //obvious, but with fixed size:
  char buffer[32];
  //what I'd like
  uint8_t buffLength;
  char *buffer;
} Ringbuffer;

//By concept...
Ringbuffer myRBs[3];
char rs485out[64];
char rs485in[16];
myRBs[0].buffLength=64;
myRBs[0].buffer = &rs485out;
myRBs[1].buffLength=16;
myRBs[1].buffer = &rs485in;

# warning: assignment from incompatible pointer type at ( .. = &rs485out)