ATtiny2313: 250 kBd  (UCSRA.U2X gesetzt):

Umin[V]  f[MHz]  UBRR  I[mA]    I[mA] @ 4.0 V
2.7      10.00     4    3.2      4.5
3.1      12.00     5    4.5      5.3
3.4      14.00     6    5.8      6.1
3.8      16.00     7    6.4      6.9