Serial communications is the process of sending data one bit at one time, sequentially, over a communication channel or computer bus. Serial communications is used for all long haul communications and most computer networks, where the cost of cable and synchronization difficulties make parallel communications impractical. Serial transmission is commonly used with modems and for non-networked communication between computers, terminals and other devices. The Universal Asynchronous Receiver/Transmitter (UART) controller is the key component of the serial communications subsystem of a computer. The UART takes bytes of data and transmits the individual bits in a sequential fashion. At the destination, a second UART re-assembles the bits into complete bytes.
[...] Bit 6 Res: Reserved Bit: This bit is a reserved bit in the AT90S8515 and will always read as zero. Bit 5 ACO: Analog Comparator Output : ACO is directly connected to the comparator output. Bit 4 ACI: Analog Comparator Interrupt Flag: This bit is set (one) when a comparator output event triggers the interrupt mode defined by ACI1 and ACI0. The Analog Comparator Interrupt routine is executed if the ACIE bit is set (one) and the I-bit in SREG is set (one). [...]
[...] Bit rate is a measure of bit transmitted per second, “bits per second" UNIVERSAL ASYNCHRONOUS RECEIVER/TRANSMITEER (UART) It is an integrated circuit which handles the conversion between serial and parallel data. Features of UART Baud Rate Generator that can Generate a large Number of Baud Rates (bps) High Baud Rates at Low XTAL Frequencies 8 or 9 Bits Data Noise Filtering Overrun Detection Framing Error Detection False Start Bit Detection Three separate Interrupts on TX Complete, TX Data Register Empty and RX Complete A block schematic of the UART transmitter Bit 4 FE: Framing Error This bit is set if a Framing Error condition is detected, i.e., when the stop bit of an incoming character is zero. [...]
[...] When the receiver is disabled, the RXC, OR and FE status flags cannot become set. If these flags are set, turning off RXEN does not cause them to be cleared. Bit 3 TXEN: Transmitter Enable : This bit enables the UART transmitter when set(one). When disabling the transmitter while transmitting a character, the transmitter is not disabled before the character in the shift register plus any following character in UDR has been completely transmitted. Bit 2 CHR9: 9-bit Characters: When this bit is set (one) transmitted and received characters are 9 bits long plus start and stop bits. [...]
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