TL16CP754C Datasheet, PDF (16/49 Pages) Texas Instruments – QUAD UARTS WITH 64-BYTE FIFO

TL16CP754C, TL16CM754C, TL16C754C
SLLS644E – DECEMBER 2007 – REVISED MAY 2010
www.ti.com
Programmable Baud Rate Generator
The '754C UART contains a programmable baud generator that divides reference clock by a divisor in the range
between 1 and (216−1). The output frequency of the baud rate generator is 16× the baud rate. An additional
divide-by-4 prescaler is also available and can be selected by the CLKSEL pin or MCR[7], as shown in the
following. The formula for the divisor is:
Divisor = (XTAL crystal input frequency / prescaler) / (desired baud rate X 16)
Where
prescaler =
1 when CLKSEL = high during reset, or MCR[7] is set to 0 after reset
4 when CLKSEL = low during reset, or MCR[7] is set to 1 after reset
Figure 9 shows the internal prescaler and baud rate generator circuitry.
XTAL1
XTAL2
Internal
Oscillator
Logic
Prescaler Logic
(Divide By 1)
Input Clock
Prescaler Logic
(Divide By 4)
MCR[7] = 0
Reference
Clock
Bandrate
Generator
Logic
MCR[7] = 1
Internal
Bandrate Clock
For Transmitter
and Receiver
Figure 9. Prescaler and Baud Rate Generator Block Diagram
DLL and DLH must be written to in order to program the baud rate. DLL and DLH are the least significant and
most significant byte of the baud rate divisor. If DLL and DLH are both zero, the UART is effectively disabled, as
no baud clock is generated. The programmable baud rate generator is provided to select both the transmit and
receive clock rates. Table 5 and Table 6 show the baud rate and divisor correlation for the crystal with frequency
1.8432 MHz and 3.072 MHz, respectively.
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