SH7041A datasheet(564/923 Pages) RENESAS

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Figure 14.19 shows an example of SCI transmit operation.

Bit 0

Bit 1

Bit 7

Bit 0

Bit 1

Bit 6

Synchroni-

zation clock

Serial data

Transmit direction

Bit 7

TxI interrupt

handler writes

data in TDR and

clears TDRE to 0

1 frame

TxI

request

TxI

request

TDRE

TEND

LSB

MSB

TEI

request

Figure 14.19 Example of SCI Transmit Operation

SCI serial transmission operates as follows.

1.The SCI monitors the TDRE bit in the SSR.When TDRE is cleared to 0 the SCI recognizes

that the transmit data register (TDR) contains new data and loads this data from the TDR into

the transmit shift register (TSR).

2.After loading the data from the TDR into the TSR, the SCI sets the TDRE bit to 1 and starts

transmitting. If the transmit-data-empty interrupt enable bit (TIE) in the SCR is set to 1, the

SCI requests a transmit-data-empty interrupt (TxI) at this time.

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

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

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

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

data from the TDR into the TSR, then begins serial transmission of the next frame. If TDRE is

1, the SCI sets the TEND bit in the SSR to 1, transmits the MSB, then holds the transmit data

pin (TxD) in the MSB state. If the transmit-end interrupt enable bit (TEIE) in the SCR is set to

1, a transmit-end interrupt (TEI) is requested at this time.

4.After the end of serial transmission, the SCK pin is held in the high state.

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