STV3550 datasheet(123/144 Pages) STMICROELECTRONICS

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This gives good granularity, and hence low baud rate deviation errors, at high baud rate

frequencies.

7.8.6

Interrupt Control

Each ASC contains two registers that are used to control interrupts, the status register

(ASC_n_Status) and the interrupt enable register (ASC_n_IntEnable). The status bits in the

ASC_n_Status register show the cause of any interrupt. The interrupt enable register allows certain

interrupt causes to be masked. Interrupts will occur when a status bit is 1 (high) and the

corresponding bit in the ASC_n_IntEnable register is 1.

The ASC interrupt signal is generated from the OR of all interrupt status bits after they have been

ANDed with the corresponding enable bits in the ASC_n_IntEnable register, as shown in

Figure 73.

The status bits cannot be reset by software because the ASC_n_Status register cannot be written

to directly. Status bits are reset by operations performed by the interrupt handler:

●

Transmitter interrupt status bits (TxEmpty, TxHalfEmpty) are reset when a character is written

to the transmitter buffer

●

Receiver interrupt status bit (RxBufFull) is reset when a character is read from the receive

buffer

●

ParityError and FrameError status bits are reset when all characters containing errors have

been read from the receive input buffer

●

The OverrunError status bit is reset when a character is read from ASC_n_RxBuffer

7.8.6.1 Using the ASC Interrupts when FIFOs are Disabled (Double-buffered Operation)

The transmitter generates two interrupts; this provides advantages for the servicing software. For

normal operation (i.e. other than the error interrupt) 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 ASC_n_TxBuffer to the transmit shift

●

TxEmpty is activated before the last bit of a frame is transmitted

●

RxBufFull is activated when the received frame is moved to ASC_n_RxBuffer

STV3550 Datasheet(PDF) 123 Page - STMicroelectronics