Hitachi H8/3827R Series Hardware Manual page 280

RDR
RSR (reception in progress)
RXD pin
3x
RDRF = 0
TDR (next transmit data)
TSR (transmission in progress)
TXD pin
3x
TDRE = 0
TDR
TSR (transmission in progress)
TXD pin
3x
TEND = 0
274
Figure 10.2 (a) RDRF Setting and RXI Interrupt
Figure 10.2 (b) TDRE Setting and TXI Interrupt
Figure 10.2 (c) TEND Setting and TEI Interrupt
RDR
RSR↑ (reception completed, transfer)
RXD pin
3x
RDRF ← 1
(RXI request when RIE = 1)
TDR
TSR↓ (transmission completed, transfer)
TXD pin
3x
TDRE ← 1
(TXI request when TIE = 1)
TDR
TSR (reception completed)
TXD pin
3x
TEND ← 1
(TEI request when TEIE = 1)