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16C2850 参数 Datasheet PDF下载

16C2850图片预览
型号: 16C2850
PDF下载: 下载PDF文件 查看货源
内容描述: 双UART,具有128字节FIFO的和RS- 485半双工控制 [DUAL UART WITH 128-byte FIFO’s AND RS-485 HALF DUPLEX CONTROL]
分类和应用: 先进先出芯片
文件页数/大小: 44 页 / 670 K
品牌: EXAR [ EXAR CORPORATION ]
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XR16C2850  
ingtheremovalofadatabyte, theusershouldrecheck  
LSR bit-0 for additional characters. A Receive Time  
Out will not occur if the receive FIFO is empty. The  
time out counter is reset at the center of each stop bit  
received or each time the receive holding register  
(RHR) is read. The actual time out value is T (Time out  
length in bits) = 4 X P (Programmed word length) + 12.  
To convert the time out value to a character value, the  
user has to consider the complete word length, includ-  
ing data information length, start bit, parity bit, and the  
size of stop bit, i.e., 1X, 1.5X, or 2X bit times.  
externally between the XTAL1 and XTAL2 pins, with  
an external 1 Mresistor across it. Alternatively, an  
external clock can be connected to the XTAL1 pin to  
clock the internal baud rate generator for standard or  
custom rates.  
The generator divides the input 16X clock by any  
divisor from 1 to 216 -1. The 2850 divides the basic  
crystal or external clock by 16. Further division of this  
16X clock provides two table rates to support low and  
high data rate applications using the same system  
design. The two rate tables are selectable through the  
internal register, MCR bit-7. Setting MCR bit-7 to a  
logic 1 provides an additional divide by 4 whereas,  
setting MCR bit-7 to a logic 0 only divides by 1 (see  
Table 4 and Figure 11). The frequency of the -  
BAUDOUT output pin is exactly 16X (16 times) of the  
selected baud rate (-BAUDOUT =16 x Baud Rate).  
Customized Baud Rates can be achieved by selecting  
the proper divisor values for the MSB and LSB sec-  
tions of baud rate generator.  
Example -A: If the user programs a word length of 7,  
with no parity and one stop bit, the time out will be:  
T=4X7(programmedwordlength)+12=40bittimes.  
The character time will be equal to 40 / 9 = 4.4  
characters, or as shown in the fully worked out ex-  
ample: T = [(programmed word length = 7) + (stop bit  
= 1) + (start bit = 1) = 9]. 40 (bit times divided by 9) =  
4.4 characters.  
Example -B: If the user programs the word length = 7,  
with parity and one stop bit, the time out will be:  
T=4X7(programmedwordlength)+12=40bittimes.  
Character time = 40 / 10 [ (programmed word length  
= 7) + (parity = 1) + (stop bit = 1) + (start bit = 1)] = 4  
characters.  
Crystal oscillator connection  
Programmable Baud Rate Generator  
The 2850 supports high speed modem technologies  
that have increased input data rates by employing  
data compression schemes. For example a 33.6Kbps  
modem that employs data compression may require a  
115.2Kbpsinputdatarate.A128.0KbpsISDNmodem  
that supports data compression may need an input  
data rate of 460.8Kbps. The 2850 can support a  
standard data rate of 921.6Kbps.  
R1  
50-120  
R2  
1M  
X1  
A single baud rate generator is provided for the  
transmitter and receiver, allowing independent TX/RX  
channel control. The programmable Baud Rate  
Generator is capable of accepting an input clock up to  
24 MHz, as required for supporting a 1.5Mbps data  
rate. The 2850 can be configured for internal or  
external clock operation. For internal clock oscillator  
operation, an industry standard microprocessor crys-  
tal (parallel resonant 22-33 pF load) is connected  
1.8432 MHz  
C1  
22pF  
C2  
33pF  
Rev. 1.00P  
12  
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