Hitachi H8/3664 Hardware Manual page 286

RDR
RSR (reception in progress)
RXD pin
RDRF = 0
TDR (next transmit data)
TSR (transmission in progress)
TXD pin
TDRE = 0
TDR
TSR (transmission in progress)
TXD pin
TEND = 0
270
Figure 14.2 (a) RDRF Setting and RXI Interrupt
Figure 14.2 (b) TDRE Setting and TXI Interrupt
Figure 14.2 (c) TEND Setting and TEI Interrupt
RDR
↑
RSR (reception completed, transfer)
RXD pin
RDRF ← 1
(RXI request when RIE = 1)
TDR
↓
TSR (transmission completed, transfer)
TXD pin
TDRE ← 1
(TXI request when TIE = 1)
TDR
TSR (reception completed)
TXD pin
TEND ← 1
(TEI request when TEIE = 1)