XR17V352IB-0A-EVB Datasheet, PDF (59/64 Pages) Exar Corporation – HIGH PERFORMANCE DUAL PCI EXPRESS UART

XR17V352
REV. 1.0.4
HIGH PERFORMANCE DUAL PCI EXPRESS UART
EFR[3:0]: Software Flow Control Select
Combinations of software flow control can be selected by programming these bits, as shown in Table 19.
TABLE 19: SOFTWARE FLOW CONTROL FUNCTIONS
EFR BIT [3]
EFR BIT [2] EFR BIT [1] EFR BIT [0] TRANSMIT AND RECEIVE SOFTWARE FLOW CONTROL
0
0
0
0
No TX and RX flow control (default and reset)
0
0
X
X
No transmit flow control
1
0
X
X
Transmit Xon1, Xoff1
0
1
X
X
Transmit Xon2, Xoff2
1
1
X
X
Transmit Xon1 and Xon2, Xoff1 and Xoff2
X
X
0
0
No receive flow control
X
X
1
0
Receiver compares Xon1, Xoff1
X
X
0
1
Receiver compares Xon2, Xoff2
1
0
1
1
Transmit Xon1, Xoff1
Receiver compares Xon1 or Xon2, Xoff1 or Xoff2
0
1
1
1
Transmit Xon2, Xoff2
Receiver compares Xon1 or Xon2, Xoff1 or Xoff2
1
1
1
1
Transmit Xon1 and Xon2, Xoff1 and Xoff2
Receiver compares Xon1 and Xon2, Xoff1 and Xoff2
0
0
1
1
No transmit flow control
Receiver compares Xon1 and Xon2, Xoff1 and Xoff2
Software flow control can not be used when the Auto RS-485 Half-Duplex Direction Control feature is enabled
(FCTR[5]=1). With this feature enabled, the RTS#/DTR# output controls the direction of the half-duplex RS-
485 transceiver. The RTS#/DTR# output changes the direction of the half-duplex transceiver to the transmit
mode when data is being transmitted from the UART on the TX output. However, the RTS#/DTR# output will
remain in the receive direction if the TX FIFO is empty and the RX FIFO triggers an XON or XOFF character to
be transmitted.
4.15 TXCNT[7:0]: Transmit FIFO Level Counter - Read Only
Transmit FIFO level byte count from 0x00 (0 bytes) to 0xFF (255 or 256 bytes). This 8-bit register gives an
indication of the number of characters in the transmit FIFO. The FIFO level Byte count register is read only.
The user can take advantage of the FIFO level byte counter for faster data loading to the transmit FIFO, which
reduces CPU bandwidth requirements.
4.16 TXTRG [7:0]: Transmit FIFO Trigger Level - Write Only
An 8-bit value written to this register sets the TX FIFO trigger level from 0x00 (zero) to 0xFF (255). The TX
FIFO trigger level generates an interrupt whenever the data level in the transmit FIFO falls below this preset
trigger level.
4.17 RXCNT[7:0]: Receive FIFO Level Counter - Read Only
Receive FIFO level byte count from 0x00 (0 bytes) to 0xFF (255 or 256 bytes). It gives an indication of the
number of characters in the receive FIFO. The FIFO level byte count register is read only. The user can take
advantage of the FIFO level byte counter for faster data unloading from the receiver FIFO, which reduces CPU
bandwidth requirements.
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