參數(shù)資料
型號(hào)： XR17V252IM-0A-EVB
廠商： Exar Corporation
文件頁數(shù)： 21/69頁
文件大?。?/td> 0K
描述： EVAL BOARD FOR XR17V252 100TQFP
標(biāo)準(zhǔn)包裝： 1
系列： *
XR17V252
28
66 MHZ PCI BUS DUAL UART WITH POWER MANAGEMENT SUPPORT
REV. 1.0.2
4.0
UART
There are 2 UARTs channel [1:0] in the V252. Each has its own 64-byte of transmit and receive FIFO, a set of
16550 compatible control and status registers, and a baud rate generator for individual channel data rate
setting. Eight additional registers per UART were added for the EXAR enhanced features.
4.1
Programmable Baud Rate Generator with Fractional Divisor
Each UART has its own Baud Rate Generator (BRG) with a prescaler for the transmitter and receiver. The
prescaler is controlled by a software bit in the MCR register. The MCR register bit [7] sets the prescaler to
divide the input crystal or external clock by 1 or 4. The output of the prescaler clocks to the BRG. The BRG
further divides this clock by a programmable divisor between 1 and (216 - 0.0625) in increments of 0.0625 (1/
16) to obtain a 16X or 8X sampling clock of the serial data rate. The sampling clock is used by the transmitter
for data bit shifting and receiver for data sampling. The BRG divisor (DLL, DLM and DLD registers) defaults to
a random value upon power up. Therefore, the BRG must be programmed during initialization to the operating
data rate. The DLL and DLM registers provide the integer part of the divisor and the DLD register provides the
fractional part of the divisor. Only the four lower bits of the DLD are implemented and they are used to select a
value from 0 (for setting 0000) to 0.9375 or 15/16 (for setting 1111). Programming the Baud Rate Generator
Registers DLL, DLM and DLD provides the capability for selecting the operating data rate. Table 12 shows the
standard data rates available with a 14.7456 MHz crystal or external clock at 16X clock rate. If the pre-scaler is
used (MCR bit [7] = 1), the output data rate will be 4 times less than that shown in Table 12. At 8X sampling
rate, these data rates would double. Also, when using 8X sampling mode, please note that the bit-time will
have a jitter (+/- 1/16) whenever the DLD is an odd number. When using a non-standard data rate crystal or
external clock, the divisor value can be calculated with the following equation(s):
The closest divisor that is obtainable in the V252 can be calculated using the following formula:
In the formulas above, please note that:
TRUNC (N) = Integer Part of N. For example, TRUNC (5.6) = 5.
ROUND (N) = N rounded towards the closest integer. For example, ROUND (7.3) = 7 and ROUND (9.9) = 10.
Required Divisor (decimal) = (XTAL1 clock frequency / prescaler) / (serial data rate x 16), WITH 8XMODE [7:0] IS 0
Required Divisor (decimal) = (XTAL1 clock frequency / prescaler / (serial data rate x 8), WITH 8XMODE [7:0] IS 1
ROUND( (Required Divisor - TRUNC (Required Divisor) )*16)/16 + TRUNC (Required Divisor), where
DLM = TRUNC( Required Divisor) >> 8
DLL = TRUNC (Required Divisor) & 0xFF
DLD = ROUND ( (Required Divisor-TRUNC(Required Divisor) )*16)
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
XR17V252IM-F 功能描述:UART 接口集成電路 66MHz Dual PCI UART RoHS:否 制造商:Texas Instruments 通道數(shù)量:2 數(shù)據(jù)速率:3 Mbps 電源電壓-最大:3.6 V 電源電壓-最小:2.7 V 電源電流:20 mA 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝 / 箱體:LQFP-48 封裝:Reel
XR17V252IMTR-F 制造商:Exar Corporation 功能描述:UART 2-CH 64Byte FIFO 3.3V 100-Pin TQFP T/R 制造商:Exar Corporation 功能描述:XR17V252IMTR-F
XR17V254 制造商:EXAR 制造商全稱:EXAR 功能描述:66MHZ PCI BUS QUAD UART WITH POWER MANAGEMENT SUPPORT
XR17V254_08 制造商:EXAR 制造商全稱:EXAR 功能描述:66MHZ PCI BUS QUAD UART WITH POWER MANAGEMENT SUPPORT
XR17V254IV 制造商:EXAR 制造商全稱:EXAR 功能描述:66MHZ PCI BUS QUAD UART WITH POWER MANAGEMENT SUPPORT
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