HD643303x Hitachi, HD643303x Datasheet - Page 374

• Manufacturer Part Number: HD643303x
• Description: Hitachi Microcomputer
• Manufacturer: Hitachi

In transmitting serial data, the SCI operates as follows.
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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.
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 in 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,
holds the TxD pin in the MSB state. If the TEIE bit in SCR is set to 1, 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.
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