Datasheet

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SLLS165G − JANUARY 1994 − REVISED MARCH 2006
28
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
PRINCIPLES OF OPERATION
programmable baud rate generator (continued)
Table 11. Baud Rates Using an 16-MHz Clock
BAUD RATE
DESIRED
DIVISOR (N) USED TO
GENERATE 16× CLOCK
PERCENT ERROR DIFFERENCE
BETWEEN DESIRED AND ACTUAL
50 20000 0
75 13334 0.00
110 9090 0.01
134.5 7434 0.01
150 6666 0.01
300 3334 −0.02
600 1666 0.04
1200 834 −0.08
1800 554 0.28
2000 500 0.00
2400 416 0.16
3600 278 −0.08
4800 208 0.16
7200 138 0.64
9600 104 0.16
19200 52 0.16
38400 26 0.16
56000 18 −0.79
128000 8 −2.34
256000 4 −2.34
512000 2 −2.34
1000000 1 0.00
receiver
Serial asynchronous data is input into the RXx terminal. The ACE continually searches for a high-to-low
transition from the idle state. When the transition is detected, a counter is reset and counts the 16× clock to
7 1/2, which is the center of the start bit. The start bit is valid when the RXx is still low. Verifying the start bits
prevents the receiver from assembling a false data character due to a low going noise spike on the RXx input.
The LCR determines the number of data bits in a character (LCR0, LCR1). When parity is enabled, LCR3 and
the polarity of parity LCR4 are needed. Status for the receiver is provided in the LSR. When a full character is
received including parity and stop bits, the data received indicator in LSR0 is set. The CPU reads the RBR, which
clears LSR0. If the character is not read prior to a new character transfer from the RSR to the RBR, the overrun
error status indicator is set in LSR1. If there is a parity error, the parity error is set in LSR2. If a stop bit is not
detected, a framing error indicator is set in LSR3.
In the FIFO mode operation, the data character and the associated error bits are stored in the receiver FIFO.
If the data into RXx is a symmetrical square wave, the center of the data cells occurs within ±3.125% of the actual
center, providing an error margin of 46.875%. The start bit can begin as much as one 16× clock cycle prior to
being detected.