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SC16IS752 Datasheet(PDF) 34 Page - NXP Semiconductors |
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SC16IS752 Datasheet(HTML) 34 Page - NXP Semiconductors |
34 / 59 page ![]() SC16IS752_SC16IS762_7 © NXP B.V. 2008. All rights reserved. Product data sheet Rev. 07 — 19 May 2008 34 of 59 NXP Semiconductors SC16IS752/SC16IS762 Dual UART with I2C-bus/SPI interface, 64-byte FIFOs, IrDA SIR 9.3 Auto RS-485 EFCR bit 0 is used to enable the RS-485 mode (multidrop or 9-bit mode). In this mode of operation, a ‘master’ station transmits an address character followed by data characters for the addressed ‘slave’ stations. The slave stations examine the received data and interrupt the controller if the received character is an address character (parity bit = 1). To use the auto RS-485 RTS mode the software would have to disable the hardware flow control function. 9.3.1 Normal multidrop mode The 9-bit mode in EFCR (bit 0) is enabled, but not Special Character Detect (EFR bit 5). The receiver is set to Force Parity 0 (LCR[5:3] = 111) in order to detect address bytes. With the receiver initially disabled, it ignores all the data bytes (parity bit = 0) until an address byte is received (parity bit = 1). This address byte will cause the UART to set the parity error. The UART will generate a line status interrupt (IER bit 2 must be set to ‘1’ at this time), and at the same time puts this address byte in the RX FIFO. After the controller examines the byte it must make a decision whether or not to enable the receiver; it should enable the receiver if the address byte addresses its ID address, and must not enable the receiver if the address byte does not address its ID address. If the controller enables the receiver, the receiver will receive the subsequent data until being disabled by the controller after the controller has received a complete message from the ‘master’ station. If the controller does not disable the receiver after receiving a message from the ‘master’ station, the receiver will generate a parity error upon receiving another address byte. The controller then determines if the address byte addresses its ID address, if it is not, the controller then can disable the receiver. If the address byte addresses the ‘slave’ ID address, the controller take no further action; the receiver will receive the subsequent data. 9.3.2 Auto address detection If Special Character Detect is enabled (EFR[5] is set and XOFF2 contains the address byte) the receiver will try to detect an address byte that matches the programmed character in XOFF2. If the received byte is a data byte or an address byte that does not match the programmed character in XOFF2, the receiver will discard these data. Upon receiving an address byte that matches the XOFF2 character, the receiver will be automatically enabled if not already enabled, and the address character is pushed into the RX FIFO along with the parity bit (in place of the parity error bit). The receiver also generates a line status interrupt (IER bit 2 must be set to 1 at this time). The receiver will then receive the subsequent data from the ‘master’ station until being disabled by the controller after having received a message from the ‘master’ station. If another address byte is received and this address byte does not match XOFF2 character, the receiver will be automatically disabled and the address byte is ignored. If the address byte matches XOFF2 character, the receiver will put this byte in the RX FIFO along with the parity bit in the parity error bit (LSR[2]). |
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