C2K User’s Guide
5-48
Resources
The USART clears the various interrupt indications in different ways depending on the source of
the interrupt as listed below:
Receiver Line Status interrupt:
cleared by reading the Line Status Register.
Receiver Data Available interrupt:
cleared by reading the Receive Buffer Register or when the
FIFO buffer falls below the trigger level.
Time-out interrupt:
cleared by reading from the FIFO buffer.
Transmit Holding Register Empty interrupt:
cleared either by reading the Interrupt Identification
Register when it is the source of the interrupt, or by writing to the Transmit Data Register.
Modem Status interrupt:
cleared by reading the Modem Status Register.
Identification Register
USART FIFO Control Register
The USART FIFO Control Register enables and clears the transmit and receive data FIFO buffers
and sets the trigger levels.
3 - 1
ID
0b000
Interrupt Identification as highest priority—identifies the interrupt with
highest priority.
0b011 (1st) = receiver line status
0b010 (2nd) = receiver data available
0b001 (3rd) = Transmit Holding Register empty
0b000 (4th) = modem status
0
NPEND
1
Interrupt Pending—indicates an USART interrupt is pending.
0 = interrupt is pending
1 = no interrupt is pending
Address offset:
USAR0x2
Access:
Write-only
Bit(s)
Field
Default
Description
7 - 6
RX_TRIG
0b00
Receive FIFO Trigger Level—sets the Receive FIFO buffer trigger
levels.
Bit(s)
Field
Default
Description
16-byte FIFO –
64-byte FIFO –
0b00 = 1 byte
0b00 = 1 byte
0b01 = 4 bytes
0b01 = 16 bytes
0b10 = 8 bytes
0b10 = 32 bytes
0b11 = 14 bytes
0b11 = 56 bytes
256-byte FIFO –
1024-byte FIFO –
0b00 = 1 byte
0b00 = 1 byte
0b01 = 32 bytes
0b01 = 64 bytes
0b10 = 64 bytes
0b10 = 128 bytes
0b11 = 128 bytes
0b11 = 256 bytes
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