H8SLASH3021 datasheet(391/712 Pages) RENESAS

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11. Serial Communication Interface

Rev.2.00 Mar. 22, 2007 Page 367 of 684

REJ09B0352-0200

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 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:

⎯ Start bit:

One 0 bit is output.

⎯ Transmit data:

7 or 8 bits are output, LSB first.

⎯ 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.

⎯ Stop bit:

One or two 1 bits (stop bits) are output.

⎯ Mark state:

Output of 1 continues until the start bit of the

next transmit data.

• 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 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 11.6 shows an example of SCI transmit operation in asynchronous mode.

Start

bit

0/1

Stop

bit

Data

Parity

bit

Start

bit

0/1

Stop

bit

Data

Parity

bit

Idle (mark)

state

TDRE

TEND

TXI

interrupt

request

TXI interrupt handler

writes data in TDR and

clears TDRE flag to 0

TXI

interrupt

request

1 frame

TEI interrupt request

Figure 11.6 Example of SCI Transmit Operation in Asynchronous Mode

(8-Bit Data with Parity and 1 Stop Bit)

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