Motorola MPC823e

Communication Processor Module
16-162 MPC823e REFERENCE MANUAL MOTOROLA
BRGs
COMMUNICATION
16
PROCESSOR MODULE
16.8.3 UART Baud Rate Examples
For synchronous communication using the internal baud rate generator, the BRGOx output
clock must never be faster than the system frequency divided by 2. So, with a 25MHz
system frequency, the maximum BRGOx output clock rate is 12.5MHz. You must program
the UART to 16× oversampling when using a serial communication controller in UART
mode. On the MPC823e, 8× and 32× options are also available. Assuming 16×
oversampling is chosen in the UART, a data rate of 25MHz ÷ 16 = 1.5625Mb/sec is the
maximum possible UART speed. Putting this together, the following formula must be used
to calculate the bit rate based on a particular baud rate generator configuration for a UART:
async baud rate = (BRGCLK, CLK2 or CLK4) ÷ (clock divider + 1) ÷ (1 or 16
depending on the DIV16 bit) ÷ (8, 16, or 32 according to the
RDCR and TDCR fields in the GSMR_L register).
The following table lists typical bit rates of asynchronous communication. The internal clock
rate is assumed to be 16× the baud rate.
Table 16-23. Typical Baud Rates of Asynchronous Communication
BAUD
RATES
MPC823e SYSTEM FREQUENCY (MHz)
20 25 24.5760
DIV16 DIV ACTUAL
FREQUENCY
DIV16 DIV ACTUAL
FREQUENCY
DIV16 DIV ACTUAL
FREQUENCY
50 1 1561 50.02 1 1952 50 1 1919 50
75 1 1040 75.05 1 1301 75 1 1279 75
150 1 520 149.954 1 650 150 1 639 150
300 1 259 300.48 1 324 300.5 1 319 300
600 0 2082 600.09 0 2603 600 0 2559 600
1200 0 1040 1200.7 0 1301 1200 0 1279 1200
2400 0 520 2399.2 0 650 2400.1 0 639 2400
4800 0 259 4807.7 0 324 4807.69 0 319 4800
9600 0 129 9615.4 0 162 9585.9 0 159 9600
19200 0 64 19231 0 80 19290 0 79 19200
38400 0 32 37879 0 40 38109 0 39 38400
57600 0 21 56818 0 26 57870 0 26 56889
115200 0 10 113636 0 13 111607 0 12 118154
NOTE: All values are decimal.