STR720 datasheet(176/401 Pages) STMICROELECTRONICS

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STR720 - UART

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16.3.7

Using the ASC interrupts when fifos are disabled

When fifos are disabled, the ASC provides three interrupt requests to control data exchange

via the serial channel:

• TxHalfEmpty is activated when data is moved from ASCTxBuffer to the txshift register.

• TxEmpty is activated before the stop bit is transmitted.

• RxBufNotEmpty is activated when the received frame is moved to ASCRxBuffer.

For single transfers it is sufficient to use the transmitter interrupt (TxEmpty), which indicates

that the previously loaded data has been transmitted, except for the stop bit.

For multiple back-to-back transfers using TxEmpty would leave just one stop bit time for the

handler to respond to the interrupt and initiate another transmission. Using the transmit buffer

interrupt (TxHalfEmpty) to reload transmit data allows the time to transmit a complete frame

for the service routine, as ASCTxBuffer may be reloaded while the previous data is still being

transmitted.

TxHalfEmpty is an early trigger for the reload routine, while TxEmpty indicates the

completed transmission of the data field of the frame. Therefore, software using handshake

should rely on TxEmpty at the end of a data block to make sure that all data has really been

transmitted.

16.3.8

Using the ASC interrupts when fifos are enabled

To transmit a large number of characters back to back, the driver routine would write 16

characters to ASCTxBuffer, then every time a TxHalfEmpty interrupt fired, it would write 8

more. When it had nothing more to send, a TxEmpty interrupt would tell it when everything

has been transmitted.

When receiving, the driver could use RxBufNotEmpty to interrupt every time a character

came in. Alternatively, if data is coming in back-to-back, it could use RxHalfFull to interrupt it

when there was at least 8 characters in the rxfifo to read. It would have as long as it takes to

receive 8 characters to respond to this interrupt before data would overrun. If less than eight

character streamed in, and no more were received for at least a timeout period, the driver

could be woken up by one of the two timeout interrupts, TimeoutNotEmpty or TimeoutIdle.

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