st20-gp6 STMicroelectronics, st20-gp6 Datasheet - Page 88

• Manufacturer Part Number: st20-gp6
• Description: Gps Processor
• Manufacturer: STMicroelectronics

ST20-GP6
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.
15.4.2 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 RxBufFull to interrupt every time a character came in. Alter-
natively, 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.
15.5 ASC configuration registers
ASCBaudRate register
The ASCBaudRate register is the dual-function baud rate generator/reload register.
A read from this register returns the content of the timer, writing to it updates the reload register.
An auto-reload of the timer with the content of the reload register is performed each time the
ASCBaudRate register is written to. However, if the Run bit of the ASCControl register, see
Table 15.4, is 0 at the time the write operation to the ASCBaudRate register is performed, the
timer will not be reloaded until the first CPU clock cycle after the Run bit is 1.
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ASCBaudRate
Bit
15:0
Bit field
ReloadVal
ASC base address + #00
Write Function
16-bit reload value
Table 15.1 ASCBaudRate register format
Read Function
16-bit count value
Read/Write