Baud Rate Generator; Table 19.1. Baud Rate Generator Settings For Standard Baud Rates - Silicon Laboratories C8051F341 Product Manual

C8051F340/1/2/3/4/5/6/7/8/9/A/B/C/D

19.1. Baud Rate Generator

The UART1 baud rate is generated by a dedicated 16-bit timer which runs from the controller's core clock
(SYSCLK), and has prescaler options of 1, 4, 12, or 48. The timer and prescaler options combined allow
for a wide selection of baud rates over many SYSCLK frequencies.
The baud rate generator is configured using three registers: SBCON1, SBRLH1, and SBRLL1. The
UART1 Baud Rate Generator Control Register (SBCON1, SFR Definition 19.4) enables or disables the
baud rate generator, and selects the prescaler value for the timer. The baud rate generator must be
enabled for UART1 to function. Registers SBRLH1 and SBRLL1 contain a 16-bit reload value for the dedi-
cated 16-bit timer. The internal timer counts up from the reload value on every clock tick. On timer over-
flows (0xFFFF to 0x0000), the timer is reloaded. For reliable UART operation, it is recommended that the
UART baud rate is not configured for baud rates faster than SYSCLK/16. The baud rate for UART1 is
defined in Equation 19.1.
Baud Rate
A quick reference for typical baud rates and system clock frequencies is given in Table 19.1.

Table 19.1. Baud Rate Generator Settings for Standard Baud Rates

Target Baud Actual Baud
Rate (bps) Rate (bps)
230400 230769
115200 115385
57600
28800
14400
9600
2400
1200
230400 230769
115200 115385
57600
28800
14400
9600
2400
1200
230400 230769
115200 115385
57600
28800
14400
9600
2400
1200
214
SYSCLK
-------------------------------------------------------------------------- -
=

65536 (SBRLH1:SBRLL1) –
Equation 19.1. UART1 Baud Rate
Baud Rate
Error
0.16%
0.16%
57692 0.16%
28846 0.16%
14388 0.08%
9600 0.0%
2400 0.0%
1200 0.0%
0.16%
0.16%
57692 0.16%
28777 0.08%
14406 0.04%
9600 0.0%
2400 0.0%
1200 0.0%
0.16%
0.16%
57554 0.08%
28812 0.04%
14397 0.02%
9600 0.0%
2400 0.0%
1200 0.0%
Rev. 1.3
1
 
-- - --------------------- -

2 Prescaler
Oscillator SB1PS[1:0]
Divide (Prescaler Bits)
Factor
52 11
104 11
208 11
416 11
834 11
1250 11
5000 11
10000 11
104 11
208 11
416 11
834 11
1666 11
2500 11
10000 11
20000 11
208 11
416 11
834 11
1666 11
3334 11
5000 11
20000 11
40000 11
1
Reload Value in
SBRLH1:SBRLL1
0xFFE6
0xFFCC
0xFF98
0xFF30
0xFE5F
0xFD8F
0xF63C
0xEC78
0xFFCC
0xFF98
0xFF30
0xFE5F
0xFCBF
0xFB1E
0xEC78
0xD8F0
0xFF98
0xFF30
0xFE5F
0xFCBF
0xF97D
0xF63C
0xD8F0
0xB1E0