User's Manual

29
t
BRK
UART_RX
Figure 7: Break signal
Table 11 shows a list of commonly used Baud rates and their associated values for the Persistent Store
Key PSKEY_UART_BAUDRATE (0x204). There is no requirement to use these standard values. Any
Baud rate within the supported range can be set in the Persistent Store Key according to the formula in
Equation below.
Baud Rate =
PSKEY_UART_BAUD_RATE
0.004096
Equation 2: Baud rate calculation formula
Hex Dec
1200 0x0005 5 1.73%
2400 0x000a 10 1.73%
4800 0x0014 20 1.73%
9600 0x0027 39 -0.82%
19200 0x004f 79 0.45%
38400 0x009d 157 -0.18%
57600 0x00ec 263 0.03%
76800 0x013b 315 0.14%
115200 0x01d8 472 0.03%
230400 0x03b0 944 0.03%
460800 0x075f 1887 -0.02%
921600 0x0ebf 3775 0.00%
1382400 0x161e 5662 -0.01%
1843200 0x1d7e 7550 0.00%
2765800 0x2c3d 11325 0.00%
Persistent store values
Baud rate
Error
Table 11: UART baud rates and error values
6.1.1 UART Configuration While RESET is Active
The UART interface for WT32 while the chip is being held in reset is tri-state. This will allow the user to
daisy chain devices onto the physical UART bus. The constraint on this method is that any devices
connected to this bus must tri-state when a WT32 reset is de-asserted and the firmware begins to run.
6.1.2 UART Bypass Mode
Alternatively, for devices that do not tri-state the UART bus, the UART bypass mode on WT32 can be
used. The default state of WT32 after reset is de-asserted, this is for the host UART bus to be
connected to the WT32 UART, thereby allowing communication to WT32 via the UART.
In order to apply the UART bypass mode, a BCCMD command will be issued to WT32. Upon this,
WT32 will switch the bypass to PIO[7:4] as shown in Figure 8. Once the bypass mode has been
invoked, WT32 will enter the deep sleep state indefinitely.
In order to re-establish communication with WT32, the chip must be reset so that the default
configuration takes effect.