User's Manual

Silicon Laboratories Finland Oy
Page 20 of 45
6 UART Interface
This is a standard UART interface for communicating with other serial devices.WT41u UART interface
provides a simple mechanism for communicating with other serial devices using the RS232 protocol.
Four signals are used to implement the UART function. When WT41u is connected to another digital device,
UART_RX and UART_TX transfer data between the two devices. The remaining two signals, UART_CTS and
UART_RTS, can be used to implement RS232 hardware flow control where both are active low indicators. All
UART connections are implemented using CMOS technology and have signalling levels of 0V and VDD.
UART configuration parameters, such as data rate and packet format, are set using WT41u software.
Note:
In order to communicate with the UART at its maximum data rate using a standard PC, an accelerated serial
port adapter card is required for the PC.
Parameter
Possible values
Data rate
Minimum
1200bps (2% error)
9600bps (1% error)
Maximum
3Mbps (1% error)
Flow control
RTS/CTS or None
Parity
None, Odd or Even
Number of stop bits
1 or 2
Bits per channel
8
Table 13: Possible UART Settings
The UART interface is capable of resetting WT41u upon reception of a break signal. A break is identified by a
continuous logic low (0V) on the UART_RX terminal, as shown in Figure 10. If tBRK is longer than the value,
defined by PSKEY_HOST_IO_UART_RESET_TIMEOUT, (0x1a4), a reset will occur. This feature allows a
host to initialise the system to a known state. Also, WT41u can emit a break character that may be used to
wake the host.
Figure 11: Break Signal
Table 17 shows a list of commonly used data rates and their associated values for
PSKEY_UART_BAUD_RATE (0x204). There is no requirement to use these standard values. Any data rate
within the supported range can be set in the PS Key according to the formula in Equation 1.