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SCC2681 Datasheet(PDF) 10 Page - NXP Semiconductors |
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SCC2681 Datasheet(HTML) 10 Page - NXP Semiconductors |
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10 / 29 page  Philips Semiconductors Product data SCC2681 Dual asynchronous receiver/transmitter (DUART) 2004 Apr 06 10 shift register is lost and the overrun error status bit (SR[4] will be set-upon receipt of the start bit of the new (overrunning) character). The receiver can control the deactivation of RTS. If programmed to operate in this mode, the RTSN output will be negated (set to ‘1’) when a valid start bit was received and the FIFO is full. When a FIFO position becomes available, the RTSN output will be re-asserted (set to ‘0’) automatically. This feature can be used to prevent an overrun, in the receiver, by connecting the RTSN output to the CTSN input of the transmitting device. Receiver Reset and Disable Receiver disable stops the receiver immediately – data being assembled if the receiver shift register is lost. Data and status in the FIFO is preserved and may be read. A re-enable of the receiver after a disable will cause the receiver to begin assembling characters at the next start bit detected. A receiver reset will discard the present shift register data, reset the receiver ready bit (RxRDY), clear the status of the byte at the top of the FIFO and re-align the FIFO read/write pointers. This has the appearance of “clearing or flushing” the receiver FIFO. In fact, the FIFO is NEVER cleared! The data in the FIFO remains valid until overwritten by another received character. Because of this, erroneous reading or extra reads of the receiver FIFO will miss-align the FIFO pointers and result in the reading of previously read data. A receiver reset will re-align the pointers. Multidrop Mode Note: Please see Application Note AN10251 for more information on this feature. The DUART is equipped with a wake up mode for multidrop applications. This mode is selected by programming bits MR1A[4:3] or MR1B[4:3] to ‘11’ for Channels A and B, respectively. In this mode of operation, a ‘master’ station transmits an address character followed by data characters for the addressed ‘slave’ station. The slave stations, with receivers that are normally disabled, examine the received data stream and ‘wake up’ the CPU (by setting RxRDY) only upon receipt of an address character. The CPU compares the received address to its station address and enables the receiver if it wishes to receive the subsequent data characters. Upon receipt of another address character, the CPU may disable the receiver to initiate the process again. A transmitted character consists of a start bit, the programmed number of data bits, and Address/Data (A/D) bit, and the programmed number of stop bits. The polarity of the transmitted A/D bit is selected by the CPU by programming bit MR1A[2]/MR1B[2]. MR1A[2]/MR1B[2] = 0 transmits a zero in the A/D bit position, which identifies the corresponding data bits as data while MR1A[2]/MR1B[2] = 1 transmits a one in the A/D bit position, which identifies the corresponding data bits as an address. The CPU should program the mode register prior to loading the corresponding data bits into the THR. In this mode, the receiver continuously looks at the received data stream, whether it is enabled or disabled. If disabled, it sets the RxRDY status bit and loads the character into the RHR FIFO if the received A/D bit is a one (address tag), but discards the received character if the received A/D bit is a zero (data tag). If enabled, all received characters are transferred to the CPU via the RHR. In either case, the data bits are loaded into the data FIFO while the A/D bit is loaded into the status FIFO position normally used for parity error (SRA[5] or SRB[5]). Framing error, overrun error, and break detect operate normally whether or not the receive is enabled. |
Similar Part No. - SCC2681 |
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Similar Description - SCC2681 |
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