The EUSART transmits and receives data using the standard
non-return-to-zero (NRZ) format. NRZ is implemented with two levels: a Voh Mark state which
represents a ‘1
’ data bit, and a Vol Space state
which represents a ‘0
’ data bit. NRZ refers to the
fact that consecutively transmitted data bits of the same value stay at the output level of
that bit without returning to a neutral level between each bit transmission. An NRZ
transmission port idles in the Mark state. Each character transmission consists of one
Start bit followed by eight or nine data bits and is always terminated by one or more Stop
bits. The Start bit is always a space and the Stop bits are always marks. The most common
data format is eight bits. Each transmitted bit persists for a period of 1/(Baud Rate). An
on-chip dedicated 8-bit/16-bit Baud Rate Generator is used to derive standard baud rate
frequencies from the system oscillator. See Table 2 for examples of baud rate configurations.
The EUSART transmits and receives the LSb first. The EUSART’s transmitter and receiver are functionally independent, but share the same data format and baud rate. Parity is not supported by the hardware, but can be implemented in software and stored as the ninth data bit.