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ST16C2550 Fiches technique(PDF) 10 Page - Exar Corporation |
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ST16C2550 Fiches technique(HTML) 10 Page - Exar Corporation |
10 / 34 page ST16C2550 10 Rev. 3.20 ing the removal of a data byte, the user should recheck 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, including data information length, start bit, parity bit, and the size of stop bit, i.e., 1X, 1.5X, or 2X bit times. Example -A: If the user programs a word length of 7, with no parity and one stop bit, the time out will be: T = 4 X 7( programmed word length) +12 = 40 bit times. 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 = 4 X 7(programmed word length) + 12 = 40 bit times. Character time = 40 / 10 [ (programmed word length = 7) + (parity = 1) + (stop bit = 1) + (start bit = 1) = 4 characters. Programmable Baud Rate Generator The 2550 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 115.2Kbps input data rate. A 128.0Kbps ISDN modem that supports data compression may need an input data rate of 460.8Kbps. The 2550 can support a standard data rate of 921.6Kbps. Single baud rate generator is provided for the trans- mitter and receiver, allowing independent TX/RX channel control. The programmable Baud Rate Gen- erator is capable of accepting an input clock up to 24 MHz, as required for supporting a 1.5Mbps data rate. The 2550 can be configured for internal or external clock operation. For internal clock oscillator opera- tion, an industry standard microprocessor crystal (par- allel resonant/ 22-33 pF load) is connected externally between the XTAL1 and XTAL2 pins, with an external 1 MΩ resistor 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. (see Baud Rate Generator Programming). The generator divides the input 16X clock by any divisor from 1 to 216 -1. The 2550 divides the basic external clock by 16. The basic 16X clock provides table rates to support standard and custom applica- tions using the same system design. The rate table is configured via the DLL and DLM internal register functions. Customized Baud Rates can be achieved by selecting the proper divisor values for the MSB and LSB sections of baud rate generator. Programming the Baud Rate Generator Registers DLM (MSB) and DLL (LSB) provides a user capability for selecting the desired final baud rate. The example in Table 4 below, shows the selectable baud rate table available when using a 1.8432 MHz external clock input. Crystal oscillator connection C1 22pF C2 33pF X1 1.8432 MHz R1 50-120 R2 1M |
Numéro de pièce similaire - ST16C2550 |
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Description similaire - ST16C2550 |
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