3 theory of operation, Figure 89. example uart data frame, Figure 90. nrz bit encoding example - (0100 1011) – Intel CONTROLLERS 413808 User Manual

Page 662: 89 example uart data frame, 90 nrz bit encoding example – (0100 1011), Interrupts and polling

Intel

413808 and 413812—UARTs

Intel

413808 and 413812 I/O Controllers in TPER Mode

Developer’s Manual

October 2007

662

Order Number: 317805-001US

13.3

Theory of Operation

The format of a UART data frame is shown in

Figure 89

Each data frame is between 7 bits and 12 bits long, depending on the size of data

programmed and when parity and stop bits are enabled. The frame begins with a start

bit that is represented by a high-to-low transition. Next, five to eight bits of data are

transmitted, beginning with the least significant bit. An optional parity bit follows,

which is set when even parity is enabled and an odd number of ones exist within the

data byte; or when odd parity is enabled and the data byte contains an even number of

ones. The data frame ends with one, one-and-one-half or two stop bits (as

programmed by the user), which is represented by one or two successive bit periods of

a logic one.
NRZ coding can be used by the UART to represent individual bit values. NRZ coding is

enabled when Interrupt Enable Register (IER) bit-5 is set to high. A one is represented

by a line transition and a zero is represented by no line transition.

Figure 90

shows the

NRZ coding of the data byte 8b 0100 1011. Note that the byte’s LSB is transmitted

first.

The unit is disabled upon reset, and users need to enable the unit by setting the UART

Unit Enable bit (UUE, bit-6) of Interrupt Enable Register. When the unit is enabled, the

receiver starts looking for the start bit of a frame; the transmitter sends data to the

transmit data pin when there is data available in the transmit FIFO. Transmit data can

be written to the FIFO before the unit is enabled. When the UART is disabled, the

transmitter/receiver finishes the current byte being transmitted/received (when it is in

the middle of transmitting/receiving a byte), and stops transmitting/receiving more

data. Disabling the UART with the UUE bit does not clear transmission/reception with

the original data.
Each UART has a Transmit FIFO and a Receive FIFO each holding 64 characters of data.

There are two methods for moving data into/out of the FIFOs:

Interrupts and

Polling

Figure 89. Example UART Data Frame

Start

Bit

Data<

Parity

Bit

Stop

Bit 1

Stop

Bit 2

TXD

RXD pin

LSB

MSB

Shaded bits are optional and can be programmed by user. —>

Figure 90. NRZ Bit Encoding Example – (0100 1011)

Digital

Data

NRZ

Data

Bit

Value

LSB

MSB

B6281-01