c8051t617 Silicon Laboratories, c8051t617 Datasheet - Page 150

• Manufacturer Part Number: c8051t617
• Description: Mixed Signal Byte-programmable Eprom Mcu
• Manufacturer: Silicon Laboratories

C8051T610/1/2/3/4/5/6/7
16.1. Enhanced Baud Rate Generation
The UART0 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 16.2), 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 “18.1.3. Mode 2: 8-bit Coun-
ter/Timer with Auto-Reload” on page 172). 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 UART0 baud rate is determined by Equation 16.1.
Where T1
value). Timer 1 clock frequency is selected as described in Section “18. Timers” on page 170. A quick ref-
erence for typical baud rates and system clock frequencies is given in Table 16.1. Note that the internal
oscillator may still generate the system clock when the external oscillator is driving Timer 1.
150
CLK
is the frequency of the clock supplied to Timer 1, and T1H is the high byte of Timer 1 (reload
Detected
Start
Figure 16.2. UART0 Baud Rate Logic
RX Timer
Equation 16.1. UART0 Baud Rate
UartBaudRate
Timer 1
TH1
TL1
Overflow
Overflow
Rev. 0.3
=
------------------------------ -
(
256 T1H
T1
–
CLK
2
2
)
×
UART
1
-- -
2
RX Clock
TX Clock