REV. 1.0.3 The on-chip oscillator is designed to use an industry standard microprocessor " />
參數(shù)資料
型號(hào)： XR16V2552IL-F
廠商： Exar Corporation
文件頁(yè)數(shù)： 2/46頁(yè)
文件大?。?/td> 0K
描述： IC UART FIFO 16B DUAL 32QFN
標(biāo)準(zhǔn)包裝： 490
特點(diǎn)： *
通道數(shù)： 2，DUART
FIFO's： 16 字節(jié)
規(guī)程： RS232，RS422
電源電壓： 2.25 V ~ 3.6 V
帶自動(dòng)流量控制功能： 是
帶IrDA 編碼器/解碼器： 是
帶故障啟動(dòng)位檢測(cè)功能： 是
帶調(diào)制解調(diào)器控制功能： 是
帶CMOS： 是
安裝類(lèi)型： 表面貼裝
封裝/外殼： 32-VFQFN 裸露焊盤(pán)
供應(yīng)商設(shè)備封裝： 32-QFN 裸露焊盤(pán)（5x5）
包裝： 托盤(pán)
XR16V2552
10
HIGH PERFORMANCE DUART WITH 16-BYTE FIFO
REV. 1.0.3
The on-chip oscillator is designed to use an industry standard microprocessor crystal (parallel resonant,
fundamental frequency with 10-22 pF capacitance load, ESR of 20-120 ohms and 100 ppm frequency
tolerance) connected externally between the XTAL1 and XTAL2 pins (see Figure 4). The programmable Baud
Rate Generator is capable of operating with a crystal oscillator frequency of up to 32 MHz at 2.5V. However,
with an external clock input on XTAL1 pin, it can extend its operation up to 64 MHz (16 Mbps serial data rate)
at 3.3V with a 4X sampling rate. For further reading on the oscillator circuit please see the Application Note
DAN108 on the EXAR web site at http://www.exar.com.
2.10
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 or 4X 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
the value of ’1’ (DLL = 0x01, DLM = 0x00 and DLD = 0x00) upon reset. 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 5 shows the standard data rates available with a 24MHz 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 5. 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 non-zero and 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):
Required Divisor (decimal)=(XTAL1 clock frequency / prescaler) /(serial data rate x 16), with 16X mode DLD[5:4] = ’00’
Required Divisor (decimal) = (XTAL1 clock frequency / prescaler / (serial data rate x 8), with 8X mode DLD[5:4] = ’01’
Required Divisor (decimal) = (XTAL1 clock frequency / prescaler / (serial data rate x 4), with 4X mode DLD[5:4] = ’10’
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)
The closest divisor that is obtainable in the V2552 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.
A >> B indicates right shifting the value ’A’ by ’B’ number of bits. For example, 0x78A3 >> 8 = 0x0078.
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