C8051F120/1/2/3/4/5/6/7
264
Rev. 1.2
22.1. UART0 Operational Modes
UART0 provides four operating modes (one synchronous and three asynchronous) selected by setting configuration
bits in the SCON0 register. These four modes offer different baud rates and communication protocols. The four
modes are summarized in Table 22.1.
22.1.1. Mode 0: Synchronous Mode
Mode 0 provides synchronous, half-duplex communication. Serial data is transmitted and received on the RX0 pin.
The TX0 pin provides the shift clock for both transmit and receive. The MCU must be the master since it generates
the shift clock for transmission in both directions (see the interconnect diagram in Figure 22.3).
Data transmission begins when an instruction writes a data byte to the SBUF0 register. Eight data bits are transferred
LSB first (see the timing diagram in Figure 22.2), and the TI0 Transmit Interrupt Flag (SCON0.1) is set at the end of
the eighth bit time. Data reception begins when the REN0 Receive Enable bit (SCON0.4) is set to logic 1 and the RI0
Receive Interrupt Flag (SCON0.0) is cleared. One cycle after the eighth bit is shifted in, the RI0 flag is set and recep-
tion stops until software clears the RI0 bit. An interrupt will occur if enabled when either TI0 or RI0 are set.
The Mode 0 baud rate is SYSCLK / 12. RX0 is forced to open-drain in Mode 0, and an external pull-up will typically
be required.
Table 22.1. UART0 Modes
Mode
Synchronization
Baud Clock
Data Bits Start/Stop Bits
0
Synchronous
SYSCLK / 12
8
None
1
Asynchronous
Timer 1, 2, 3, or 4 Overflow
8
1 Start, 1 Stop
2
Asynchronous
SYSCLK / 32 or SYSCLK / 64
9
1 Start, 1 Stop
3
Asynchronous
Timer 1, 2, 3, or 4 Overflow
9
1 Start, 1 Stop
Figure 22.2. UART0 Mode 0 Timing Diagram
D1
D0
D2
D3
D4
D5
D6
D7
RX (data out)
MODE 0 TRANSMIT
D0
MODE 0 RECEIVE
RX (data in)
D1
D2
D3
D4
D5
D6
D7
TX (clk out)
TX (clk out)
Figure 22.3. UART0 Mode 0 Interconnect
Shift
Reg.
CLK
C8051Fxxx
RX
TX
DATA
8 Extra Outputs
Summary of Contents for C8051F120
Page 2: ...C8051F120 1 2 3 4 5 6 7 2 Rev 1 2 Notes ...
Page 8: ...C8051F120 1 2 3 4 5 6 7 8 Rev 1 2 26 2 Flash Programming Commands 318 26 3 Debug Support 321 ...
Page 16: ...C8051F120 1 2 3 4 5 6 7 16 Rev 1 2 Notes ...
Page 48: ...C8051F120 1 2 3 4 5 6 7 48 Rev 1 2 ...
Page 98: ...C8051F120 1 2 3 4 5 6 7 98 Rev 1 2 ...
Page 106: ...C8051F120 1 2 3 4 5 6 7 106 Rev 1 2 Notes ...
Page 183: ...C8051F120 1 2 3 4 5 6 7 Rev 1 2 183 Notes ...
Page 184: ...C8051F120 1 2 3 4 5 6 7 184 Rev 1 2 ...
Page 214: ...C8051F120 1 2 3 4 5 6 7 214 Rev 1 2 Notes ...