CP2110 Datasheet, PDF (17/26 Pages) Silicon Laboratories – SINGLE-CHIP HID USB TO UART BRIDGE

CP2110
7. Asynchronous Serial Data Bus (UART) Interface
The UART interface consists of the TX (transmit) and RX (receive) data signals as well as the optional RTS and
CTS flow control signals. The UART is programmable to support a variety of data formats and baud rates. The data
format and baud rate are set during device configuration on the PC. The data formats and baud rates available to
each interface are listed in Table 12.
Table 12. Data Formats and Baud Rates
Data Bits 5, 6, 7, and 8
Stop Bits _{1, 1.5}¹_{, and 2}
Parity Type None, Even, Odd, Mark, Space
Baud Rate _{300 bps to 1 Mbps}²
Notes:
1. 1.5 stop bits only available when using 5 data bits.
2. Baud rates above 500,000 baud not supported with 5 or 6 data bits.
The baud rate generator for the UART interface is very flexible and allows the user to request any baud rate in the
range from 300 bps to 1 Mbps. If the baud rate cannot be directly generated from the internal 24 MHz oscillator, the
device will choose the closest possible option. The actual baud rate is dictated by Equation 1 and Equation 2.
Clock Divider
=
----------------------------------------²----⁴-----^M-----^H----^z------------------------------------------
2  Prescale  Requested Baud Rate
Prescale = 4 if Requested Baud Rate  300 bps
Prescale = 1 if Requested Baud Rate  300 bps
Equation 1. Clock Divider Calculation
Actual Baud Rate = -₂----_-----_P----_r---_e----_s---_c---_a--²--_l-⁴-_e----^M_-----^HC-----^zl-_o---_c---_k-----_D----_i--_v---_i-_d---_e----_r
Prescale = 4 if Requested Baud Rate  300 bps
Prescale = 1 if Requested Baud Rate  300 bps
Equation 2. Baud Rate Calculation
Most baud rates can be generated with an error of less than 1.0%. A general rule of thumb for the majority of UART
applications is to limit the baud rate error on both the transmitter and the receiver to no more than ±2%. The clock
divider value obtained in Equation 1 is rounded to the nearest integer, which may produce an error source. Another
error source will be the 24 MHz oscillator, which is accurate to ±0.25%. Knowing the actual and requested baud
rates, the total baud rate error can be found using Equation 3.
Baud Rate Error (%) = 100  _1 – _R-----_e--^A-_q---^c-_u--^t-_eu---_s-^a--_t-^l-_e--^B-_d---^a--_B-^u---_a-^d---_u--^R-_d---^a--_R-^t--^e-_a----_t-_e--_  0.25%
Equation 3. Baud Rate Error Calculation
The UART also supports the transmission of a line break. The length of time for a line break is programmable from
1 to 125 ms, or it can be set to transmit indefinitely until a stop command is sent from the application.
Rev. 1.2
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