Silicon Laboratories C8051F340 Baud Rate Generator, Equation 19.1. UART1 Baud Rate, SBRLH1SBRLL1

C8051F340/1/2/3/4/5/6/7

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 =	---------------------------------------------------------------------------SYSCLK	⋅ 1--	⋅	---------------------1
	(65536 – (SBRLH1:SBRLL1))	2		Prescaler

Equation 19.1. UART1 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	Baud Rate	Oscillator	SB1PS[1:0]	Reload Value in
	Rate (bps)	Rate (bps)	Error	Divide	(Prescaler Bits)	SBRLH1:SBRLL1
				Factor
	230400	230769	0.16%	52	11	0xFFE6
MHz	115200	115385	0.16%	104	11	0xFFCC
	57600	57692	0.16%	208	11	0xFF98
12
	28800	28846	0.16%	416	11	0xFF30
=
	14400	14388	0.08%	834	11	0xFE5F
SYSCLK
	9600	9600	0.0%	1250	11	0xFD8F
	2400	2400	0.0%	5000	11	0xF63C
	1200	1200	0.0%	10000	11	0xEC78
	230400	230769	0.16%	104	11	0xFFCC
MHz	115200	115385	0.16%	208	11	0xFF98
	57600	57692	0.16%	416	11	0xFF30
24
	28800	28777	0.08%	834	11	0xFE5F
=
	14400	14406	0.04%	1666	11	0xFCBF
SYSCLK
	9600	9600	0.0%	2500	11	0xFB1E
	2400	2400	0.0%	10000	11	0xEC78
	1200	1200	0.0%	20000	11	0xD8F0
	230400	230769	0.16%	208	11	0xFF98
MHz	115200	115385	0.16%	416	11	0xFF30
	57600	57554	0.08%	834	11	0xFE5F
48
	28800	28812	0.04%	1666	11	0xFCBF
=
	14400	14397	0.02%	3334	11	0xF97D
SYSCLK
	9600	9600	0.0%	5000	11	0xF63C
	2400	2400	0.0%	20000	11	0xD8F0
	1200	1200	0.0%	40000	11	0xB1E0

220 Rev. 0.5