HD6473032F16 Datasheet, PDF (499/847 Pages) Renesas Technology Corp – Hardware Manual Renesas 16-Bit Single-Chip Microcomputer H8 Family/H8/300H Series

Section 13 Serial Communication Interface
In transmitting serial data, the SCI operates as follows.
1. The SCI monitors the TDRE flag in SSR. When the TDRE flag is cleared to 0 the SCI
recognizes that TDR contains new data, and loads this data from TDR into TSR.
2. After loading the data from TDR into TSR, the SCI sets the TDRE flag to 1 and starts
transmitting. If the TIE bit is set to 1 in SCR, the SCI requests a transmit-data-empty
interrupt (TXI) at this time.
Serial transmit data is transmitted in the following order from the TxD pin:
a. Start bit: One 0 bit is output.
b. Transmit data: 7 or 8 bits are output, LSB first.
c. Parity bit or multiprocessor bit: One parity bit (even or odd parity) or one
multiprocessor bit is output. Formats in which neither a parity bit nor a multiprocessor
bit is output can also be selected.
d. Stop bit: One or two 1 bits (stop bits) are output.
e. Mark state: Output of 1 bits continues until the start bit of the next transmit data.
3. The SCI checks the TDRE flag when it outputs the stop bit. If the TDRE flag is 0, the SCI
loads new data from TDR into TSR, outputs the stop bit, then begins serial transmission of
the next frame. If the TDRE flag is 1, the SCI sets the TEND flag to 1 in SSR, outputs the
stop bit, then continues output of 1 bits in the mark state. If the TEIE bit is set to 1 in SCR,
a transmit-end interrupt (TEI) is requested at this time.
Figure 13.6 shows an example of SCI transmit operation in asynchronous mode.
Start
1
bit
Data
Parity Stop Start
bit bit bit
Parity Stop
Data
bit bit
1
0 D0 D1
D7 0/1 1 0 D0 D1
D7 0/1 1
Idle (mark)
state
TDRE
TEND
TXI
TXI interrupt handler
interrupt writes data in TDR and
request clears TDRE flag to 0
TXI
interrupt
request
TEI interrupt request
1 frame
Figure 13.6 Example of SCI Transmit Operation in Asynchronous Mode
(8-Bit Data with Parity and 1 Stop Bit)
Rev. 3.00 Mar 21, 2006 page 469 of 814
REJ09B0302-0300