C8051F581-IMR Silicon Labs, C8051F581-IMR Datasheet - Page 264

• Manufacturer Part Number: C8051F581-IMR
• Description: 8-bit Microcontrollers - MCU 50MIPS 128kB 8kB SPI
• Manufacturer: Silicon Labs

Specifications of C8051F581-IMR

• Rohs: yes
• Core: 8051
• Processor Series: C8051
• Data Bus Width: 8 bit

C8051F58x/F59x
25.1. Enhanced Baud Rate Generation
The UART1 baud rate is generated by Timer 1 in 8-bit auto-reload mode. The TX clock is generated by
TL1; the RX clock is generated by a copy of TL1 (shown as RX Timer in Figure 25.2), which is not user-
accessible. Both TX and RX Timer overflows are divided by two to generate the TX and RX baud rates.
The RX Timer runs when Timer 1 is enabled, and uses the same reload value (TH1). However, an
RX Timer reload is forced when a START condition is detected on the RX pin. This allows a receive to
begin any time a START is detected, independent of the TX Timer state.
Timer 1 should be configured for Mode 2, 8-bit auto-reload (see Section “27.1.3. Mode 2: 8-bit Coun-
ter/Timer with Auto-Reload” on page 286). The Timer 1 reload value should be set so that overflows will
occur at two times the desired UART baud rate frequency. Note that Timer 1 may be clocked by one of six
sources: SYSCLK, SYSCLK / 4, SYSCLK / 12, SYSCLK / 48, the external oscillator clock / 8, or an exter-
nal input T1. For any given Timer 1 clock source, the UART1 baud rate is determined by Equation 25.1-A
and Equation 25.1-B.
Where T1
value). Timer 1 clock frequency is selected as described in Section “27. Timers” on page 283. A quick ref-
erence for typical baud rates and system clock frequencies is given in Table 25.1. Note that the internal
oscillator may still generate the system clock when the external oscillator is driving Timer 1.
264
CLK
is the frequency of the clock supplied to Timer 1, and T1H is the high byte of Timer 1 (reload
Detected
Start
A)
B)
UartBaudRate
T1_Overflow_Rate
RX Timer
Figure 25.2. UART1 Baud Rate Logic
Equation 25.1. UART1 Baud Rate
Timer 1
TH1
TL1
Overflow
Overflow
=
Rev. 1.2
1
-- -
2

=
T1_Overflow_Rate
------------------------- -
256 TH1
T1
–
CLK
2
2
UART
RX Clock
TX Clock