STV3550 datasheet(124/144 Pages) STMICROELECTRONICS

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STV3550

As shown in Figure 74,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.

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 last bit of a frame.

For multiple back-to-back transfers it is necessary to load the next data before the last bit of the

previous frame has been transmitted. The use of TxEmpty alone would leave just one stop bit time

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

interrupt (TxHalfEmpty) to signal for more data allows the service routine to load a complete frame,

as ASC_n_TxBuffer may be reloaded while the previous data is still being transmitted.

7.8.6.2 Using the ASC Interrupts when FIFOs are Enabled

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

characters to ASC_n_TxBuffer. Then every time a TxHalfEmpty interrupt fired, it would write 8

Figure 73: ASC Status and Interrupt Registers

AND

RxBufFullIE

TxEmptyIE

ParityErrorIE

FrameErrorIE

OverrunErrorIE

RxBufFull

ParityError

FrameError

OverrunError

ASC interrupt

AND

TimeoutnotEmpty

TimeoutIdle

RxHalfFull

TxFull

AND

TimeoutnotEmptyIE

TimeoutIdleIE

RxHalfFullIE

Nacked

TxEmpty

TxHalfEmpty

TxHalfEmptyIE

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