SH7040 Datasheet, PDF (564/923 Pages) Renesas Technology Corp – Renesas 32-Bit Single-Chip RISC Microprocessor SuperH RISC engine Family/SH7040 Series(CPU Core SH-2)

Figure 14.19 shows an example of SCI transmit operation.
Transmit direction
Synchroni-
zation clock
Serial data
LSB
Bit 0 Bit 1
MSB
Bit 7 Bit 0 Bit 1
Bit 6 Bit 7
TDRE
TEND
TxI
request
TxI interrupt
handler writes
data in TDR and
clears TDRE to 0
1 frame
TxI
request
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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