User's Manual

9.1.1 UART Configuration While RESET is Active

The UART interface for WT12 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 WT12reset is de-

asserted and the firmware begins to run.

9.1.2 UART Bypass Mode

Alternatively, for devices that do not tri-state the UART bus, the UART bypass mode on

WT12 can be used. The default state of WT12 after reset is de-asserted, this is for the host

UART bus to be connected to the WT12 UART, thereby allowing communication to WT12

via the UART.

In order to apply the UART bypass mode, a BCCMD command will be issued to WT12 upon

this, it will switch the bypass to PIO[7:4] as shown in Figure 6. Once the bypass mode has

been invoked, WT12 will enter the deep sleep state indefinitely.

In order to re-establish communication with WT12, the chip must be reset so that the

default configuration takes affect.

It is important for the host to ensure a clean Bluetooth disconnection of any active links

before the bypass mode is invoked. Therefore it is not possible to have active Bluetooth

links while operating the bypass mode.

WT12

Host

processor

Test

interface

RXD

CTS

RTS

TXD

Another

device

RTS

CTS

UART_TX

UART_RTS

UART_CTS

UART_RX

RESET

PIO5

PIO6

PIO7

PIO4

UART

Figure 11: UART bypass mode

9.1.3 Current Consumption in UART Bypass Mode

The current consumption for a device in UART Bypass Mode is equal to the values quoted

for a device in standby mode.