Electronic Components Datasheet Search |
|
SC28C198A1A Datasheet(PDF) 9 Page - NXP Semiconductors |
|
SC28C198A1A Datasheet(HTML) 9 Page - NXP Semiconductors |
9 / 56 page Philips Semiconductors Product specification SC28L198 Octal UART for 3.3V and 5V supply voltage 1999 Jan 14 9 value”. They may, however, be loaded by a “Gang White” or “Gang Load” command as described in the “Xon Xoff Characters” paragraph. Note: Character recognition is further described in the Minor Modes of Operation. Interrupt Control The interrupt system determines when an interrupt should be asserted thorough an arbitration (or bidding) system. This arbitration is exercised over the several systems within the OCTART that may generate an interrupt. These will be referred to as ”interrupt sources”. There are 64 in all. In general the arbitration is based on the fill level of the receiver FIFO or the empty level of the transmitter FIFO. The FIFO levels are encoded into a four bit number which is concatenated to the channel number and source identification code. All of this is compared (via the bidding or arbitration process) to a user defined ”threshold”. When ever a source exceeds the numerical value of the threshold the interrupt will be generated. At the time of interrupt acknowledge (IACKN) the source which has the highest bid (not necessarily the source that caused the interrupt to be generated) will be captured in a ”Current Interrupt Register” (CIR). This register will contain the complete definition of the interrupting source: channel, type of interrupt (receiver, transmitter, change of state, etc.), and FIFO fill level. The value of the bits in the CIR are used to drive the interrupt vector and global registers such that controlling processor may be steered directly to the proper service routine. A single read operation to the CIR provides all the information needed to qualify and quantify the most common interrupt sources. The interrupt sources for each channel are listed below. • Transmit FIFO empty level for each channel • Receive FIFO Fill level for each channel • Change in break received status for each channel • Receiver with error for each channel • Change of state on channel input pins • Receiver Watch-dog Time out Event • Xon/Xoff character recognition • Address character recognition Associated with the interrupt system are the interrupt mask register (IMR) and the interrupt status register (ISR) resident in each UART. Programming of the IMR selects which of the above sources may enter the arbitration process. Only the bidders in the ISR whose associated bit in the IMR is set to one (1) will be permitted to enter the arbitration process. The ISR can be read by the host CPU to determine all currently active interrupting conditions. For convenience the bits of the ISR may be masked by the bits of the IMR. Whether the ISR is read unmasked or masked is controlled by the setting of bit 6 in MR1. Global Registers The ”Global Registers”, 19 in all, are driven by the interrupt system. These are not real hardware devices. They are defined by the content of the CIR (Current Interrupt Register) as a result of an interrupt arbitration. In other words they are indirect registers contained in the Current Interrupt Register (CIR) which the CIR uses to point to the source and context of the OCTART sub circuit presently causing an interrupt. The principle purpose of these ”registers” is improving the efficiency of the interrupt service. The global registers and the CIR update procedure are further described in the Interrupt Arbitration system I/O Ports Each of the eight UART blocks contains an I/O section of four ports. These ports function as a general purpose post section which services the particular UART they are associated with. External clocks are input and internal clocks are output through these ports. Each of the four pins has a change of state detector which will signal a change (0 to 1 or 1 to 0) at the pin. The change of state detectors are individually enabled and may be set to cause and interrupt. These pins will normally be used for flow control hand–shaking and the interface to a modem. Their control is further described in I/O Ports section and the I/OPCR register. DETAILED DESCRIPTIONS RECEIVER AND TRANSMITTER The Octal UART has eight full-duplex asynchronous receiver/transmitters. The operating frequency for the receiver and transmitter can be selected independently from the baud rate generator, the counter , or from an external input. Registers that are central to basic full-duplex operation are the mode registers (MR0, MR1 and MR2), the clock select registers (RxCSR and TxCSR), the command register (CR), the status register (SR), the transmit holding register (TxFIFO), and the receive holding register (RxFIFO). Transmitter The transmitter accepts parallel data from the CPU and converts it to a serial bit stream on the TxD output pin. It automatically sends a start bit followed by the programmed number of data bits, an optional parity bit, and the programmed number of stop bits. The least significant bit is sent first. Each character is always ”framed” by a single start bit and a stop bit that is 9/16 bit time or longer. If a new character is not available in the TxFIFO, the TxD output remains high, the ”marking” position, and the TxEMT bit in the SR is set to 1. Transmitter Status Bits The SR (Status Register, one per UART) contains two bits that show the condition of the transmitter FIFO. These bits are TxRDY and TxEMT. TxRDY means the TxFIFO has space available for one or more bytes; TxEMT means The TxFIFO is completely empty and the last stop bit has been completed. TxEMT can not be active without TxRDY also being active. These two bits will go active upon initial enabling of the transmitter. They will extinguish on the disable or reset of the transmitter. Transmission resumes and the TxEMT bit is cleared when the CPU loads at least one new character into the TxFIFO. The TxRDY will not extinguish until the TxFIFO is completely full. The TxRDY bit will always be active when the transmitter is enabled and there is at lease one open position in the TxFIFO. The transmitter is disabled by reset or by a bit in the command register (CR). The transmitter must be explicitly enabled via the CR before transmission can begin. Note that characters cannot be loaded into the TxFIFO while the transmitter is disabled, hence it is necessary to enable the transmitter and then load the TxFIFO. It is not possible to load the TxFIFO and then enable the transmission. Note the difference between transmitter disable and transmitter reset. The transmitter may by reset by a hardware or software. The |
Similar Part No. - SC28C198A1A |
|
Similar Description - SC28C198A1A |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |