The read-write
rxctrl
register controls the operation of the receive channel. The
rxen
bit con-
trols whether the Rx channel is active. When cleared, the state of the
rxd
pin is ignored, and no
characters will be enqueued into the Rx FIFO.
The
rxcnt
field specifies the threshold at which the Rx FIFO watermark interrupt triggers.
The
rxctrl
register is reset to
0
. Characters are enqueued when a zero (low) start bit is seen.
Receive Control Register (
rxctrl
)
Register Offset
0xC
Bits
Field Name
Attr.
Rst.
Description
0
rxen
RW
0x0
Receive enable
[15:1]
Reserved
[18:16]
rxcnt
RW
0x0
Receive watermark level
[31:19]
Reserved
The
ip
register is a read-only register indicating the pending interrupt conditions, and the read-
write
ie
register controls which UART interrupts are enabled.
ie
is reset to
0
.
The
txwm
condition becomes raised when the number of entries in the transmit FIFO is strictly
less than the count specified by the
txcnt
field of the
txctrl
register. The pending bit is
cleared when sufficient entries have been enqueued to exceed the watermark.
The
rxwm
condition becomes raised when the number of entries in the receive FIFO is strictly
greater than the count specified by the
rxcnt
field of the
rxctrl
register. The pending bit is
cleared when sufficient entries have been dequeued to fall below the watermark.
UART Interrupt Enable Register (
ie
)
Register Offset
0x10
Bits
Field Name
Attr.
Rst.
Description
0
txwm
RW
0x0
Transmit watermark interrupt enable
1
rxwm
RW
0x0
Receive watermark interrupt enable
Table 58:
Receive Control Register
Table 59:
UART Interrupt Enable Register
Chapter 17 Universal Asynchronous Receiver/Transmitter
FE310-G003 Manual
© SiFive, Inc.
Page 84
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