參數(shù)資料
型號(hào): XR17V252IM-F
廠商: Exar Corporation
文件頁(yè)數(shù): 31/69頁(yè)
文件大?。?/td> 0K
描述: IC UART PCI BUS DUAL 100TQFP
標(biāo)準(zhǔn)包裝: 90
特點(diǎn): *
通道數(shù): 2,DUART
FIFO's: 64 字節(jié)
規(guī)程: RS485
電源電壓: 3.3V,5V
帶自動(dòng)流量控制功能:
帶IrDA 編碼器/解碼器:
帶故障啟動(dòng)位檢測(cè)功能:
帶調(diào)制解調(diào)器控制功能:
安裝類(lèi)型: 表面貼裝
封裝/外殼: 100-TQFP
供應(yīng)商設(shè)備封裝: 100-TQFP(14x14)
包裝: 托盤(pán)
XR17V252
37
REV. 1.0.2
66 MHZ PCI BUS DUAL UART WITH POWER MANAGEMENT SUPPORT
4.6.3
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 THR empty flag can generate a transmit empty interrupt (ISR bit [1]) when
the amount of data in the FIFO falls below its programmed trigger level (see TXTRG register). 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.
4.6.4
Auto RS485 Operation
The auto RS485 half-duplex direction control changes the behavior of the transmitter when enabled by FCTR
bit [5]. It de-asserts RTS# or DTR# 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 15. 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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