H8SLASH3021 datasheet(398/712 Pages) RENESAS

398 / 712 page

11. Serial Communication Interface

Rev.2.00 Mar. 22, 2007 Page 374 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 in SCR is set to 1, 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.

⎯ Multiprocessor bit: One multiprocessor bit (MPBT value) is output.

⎯ Stop bit:

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

⎯ Mark state:

Output of 1 bits 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 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 in SSR to 1, 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 11.11 shows an example of SCI transmit operation using a multiprocessor format.

Start

bit

0/1

Stop

bit

Data

Multi-

processor

bit

Start

bit

0/1

Stop

bit

Data

Idle (mark)

state

TDRE

TEND

TXI

request

TXI interrupt handler

writes data in TDR and

clears TDRE flag to 0

TXI

request

1 frame

TEI request

Serial

data

Multi-

processor

bit

Figure 11.11 Example of SCI Transmit Operation

(8-Bit Data with Multiprocessor Bit and One Stop Bit)

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