AN1690

Data transmission protocol

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Data transmission protocol

One of the most well known formats for low speed data transmission is the UART timing

format. It is an asynchronous protocol, typically composed of 12 bits. The timing sequence

starts with a transition from high to low. Next there are 9 data bits (8 data bits plus a parity

bit). Finally, the line remains high for one or two bits, which represents the end of the

character.

Figure 3.

Asynchronous UART sequence format

In a multipoint application, when no more data has to be sent, the line should remain high

until the next start bit. Since the active driver is disabled, and all other drivers are off, this is

not easy to achieve.

One way to solve this problem is the use of an alternate protocol (software solution). The

other way is to use fail-safe biasing (hardware solution).