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DAN-183 Datasheet(PDF) 4 Page - Exar Corporation |
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DAN-183 Datasheet(HTML) 4 Page - Exar Corporation |
4 / 5 page xr DATA COMMUNICATIONS APPLICATION NOTE DAN183 4 al bit. The table below lists the different Timer/Counter functions and how they are controlled in the XR17D15x and the XR17V25x. For a detailed description of the Timer/Counter, see the XR17V25x datasheet. 3.6 TRANSMITTER AND RECEIVER DISABLE The Transmitter and Receive can be disabled in the XR17V25x. This feature is not available in the XR17D15x. The Transmitter is disabled when MSR bit-3 = 1 (write-only). When the Transmitter is disabled, any data left or written into the TX FIFO will not be transmitted. It will resume transmission when MSR bit-3 has been reset. Similarly, the Receiver is disabled when MSR bit-2 = 1 (write-only). When the Receiver is disabled, it will ig- nore any data received during that time at the RX pin. It will receive data normally when MSR bit-2 has been reset. See the XR17V25x datasheet for complete details. 3.7 TXCHAR IMMEDIATE TXCHAR Immediate is another new feature in the XR17V25x. One byte of data can be inserted into the Trans- mit Shift Register, ahead of any data that is remaining in the TX FIFO, after the current byte has shifted out. This is done by writing to MCR bit-3 (assuming EFR bit-4 = 1) and then writing to the THR register. This fea- ture can only be used when the Transmitter has not been disabled. See the XR17V25x datasheet for complete details. 3.8 TX XON/XOFF INDICATOR In the XR17D15x, the XCHAR register would indicate which flow control character (XON or XOFF) was re- ceived last by a particular channel. If bit-0 = 1, then the last flow control character received was an XOFF. If bit-1 = 1, then the last flow control character received was an XON. In addition to that, the XR17V25x has 2 additional bits to indicate whether the last flow control character transmitted was an XON or XOFF character. If XCHAR bit-2 = 1, then the last flow control character transmitted was an XOFF character. If XCHAR bit-3 = 1, then the last flow control character transmitted was an XON character. 4.0 CONCLUSION The XR17V25x is an enhanced version of the XR17D15x with a faster PCI bus clock, higher data rate, and many new features. Because of these reasons, some hardware and software changes will be required to take advantage of the performance of the 66MHz PCI clock and the other enhanced features of the XR17V25x. TABLE 8: TIMER/COUNTER FUNCTIONS TIMER/COUNTER FUNCTION XR17D15X (BIT DRIVEN) XR17V25X (COMMAND DRIVEN) Disable Timer/Counter Interrupt TIMERCNTL[0] = 0 TIMERCNTL[3:0] = 0010 Enable Timer/Counter Interrupt TIMERCNTL[0] = 1 TIMERCNTL[3:0] = 0001 Stop or Pause Timer/Counter TIMERCNTL[1] = 0 TIMERCNTL[3:0] = 1010 Start Timer/Counter TIMERCNTL[1] = 1 TIMERCNTL[3:0] = 1001 Select Re-Triggerable Mode TIMERCNTL[2] = 0 TIMERCNTL[3:0] = 0100 Select One-Shot Mode TIMERCNTL[2] = 1 TIMERCNTL[3:0] = 0011 Select Internal Crystal Oscillator as clock source for the Timer/Counter TIMERCNTL[3] = 0 TIMERCNTL[3:0] = 0101 Select External Clock (via TMRCK input pin) as clock source for the Timer/Counter TIMERCNTL[3] = 1 TIMERCNTL[3:0] = 0110 De-Route Timer output from MPIO[0] pin TIMERCNTL[4] = 0 TIMERCNTL[3:0] = 1000 Route Timer output to MPIO[0] pin TIMERCNTL[4 = 1 TIMERCNTL[3:0] = 0111 Reset Timer - TIMERCNTL[3:0] = 1011 |
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