H8SLASH3028F datasheet(531/923 Pages) RENESAS

531 / 923 page

Rev. 2.00, 09/03, page 501 of 890

In transmitting serial data, the SCI operates as follows.

• 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.

• After loading the data from TDR to 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.

If clock output is selected, the SCI outputs eight serial clock pulses. If an external clock

source is selected, the SCI outputs data in synchronization with the input clock. Data is output

from the TxD pin n order from LSB (bit 0) to MSB (bit 7).

• The SCI checks the TDRE flag when it outputs the MSB (bit 7). If the TDRE flag is 0, the

SCI loads data from TDR into TSR and begins serial transmission of the next frame. If the

TDRE flag is 1, the SCI sets the TEND flag to 1 in SSR, and after transmitting the MSB (bit

7), holds the TxD pin in the MSB state. If the TEIE bit is set to 1 in SCR, a transmit-end

interrupt (TEI) is requested at this time

• After the end of serial transmission, the SCK pin is held in a constant state.

Figure 13.17 shows an example of SCI transmit operation.

Bit 0

Bit 1

Bit 7

Bit 0

Bit 1

Bit 6

Bit 7

Serial clock

Serial data

1 frame

TXI interrupt

request

TXI interrupt handler

writes data in TDR

and clears TDRE

flag to 0

TXI interrupt

request

TEI interrupt

request

Transmit direction

TEND

TDRE

Figure 13.17 Example of SCI Transmit Operation

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