REV. 1.4.3 5V PCI BUS OCTAL UART 29 4.2.3 Transmitter Operation in FIFO mode The host may fill the transmit FIFO with up to 64 byte" />
參數(shù)資料
型號: XR17C158CV-0A-EVB
廠商: Exar Corporation
文件頁數(shù): 22/67頁
文件大?。?/td> 0K
描述: EVAL BOARD FOR XR17C158-A 144TQF
標準包裝: 1
系列: *
xr
XR17C158
REV. 1.4.3
5V PCI BUS OCTAL UART
29
4.2.3
Transmitter Operation in FIFO mode
The host may fill the transmit FIFO with up to 64 bytes of transmit data. The THR empty flag (LSR bit-5) is set
whenever the FIFO is empty. The transmit empty interrupt (ISR bit-1) is generated when the amount of data in
the FIFO falls below its programmed trigger level (see TXTRG register) and when it empties. The transmit
empty interrupt is enabled by IER bit-1. The TSR flag (LSR bit-6) is set when TSR becomes completely empty.
Furthermore, with the RS485 half-duplex direction control enabled (FCTR bit-5=1) the source of the transmit
empty interrupt changes to TSR empty instead of THR empty. This is to ensure the RTS# output is not
changed until the last stop bit of the last character is shifted out.
4.2.4
Auto RS485 Operation
The auto RS485 half-duplex direction control changes the behavior of the transmitter when enabled by FCTR
bit-5. While transmitting, the RTS# or DTR# signal is HIGH. The RTS# or DTR# signal changes from HIGH to
LOW after a specified delay indicated in MSR[7:4] following the last stop bit of the last character that has been
transmitted. This helps in turning around the transceiver to receive the remote station’s response. The delay
optimizes the time needed for the last transmission to reach the farthest station on a long cable network before
switching off the line driver. This delay prevents undesirable line signal disturbance that causes signal
degradation. It also changes the transmitter empty interrupt to TSR empty instead of THR empty.
FIGURE 10. TRANSMITTER OPERATION IN NON-FIFO MODE
Transmit
Holding
Register
(THR)
Transmit Shift Register (TSR)
Data
Byte
L
S
B
M
S
B
THR Interrupt (ISR bit-1)
Enabled by IER bit-1
TXNOFIFO1
16X or 8X
Clock
(8XMODE
Register)
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