ST2204 datasheet(17/24 Pages) SITRONIX

17 / 24 page

ST2204

Ver 0.6

17/24

2008/11/10

4.. U

NIIV

L A

S R

EIIV

R//T

MIIT

The ST2204 integrates one universal asynchronous

receiver/transmitter (UART), which can be used to

communicate with external serial devices. Serial data is

transmitted and received at standard bit rates using the

internal baud rate generator (BGR), which is controlled by

BGR control register BCTR. FIGURE 14-1 shows the block

diagram of UART.

CPU Interface

Baud Rate

Generator

Transmitter

Receiver

TXD0

RXD0

Serial

Interface

IrDA

Interface

TXD1

RXD1

FIGURE 14-1 UART Block Diagram

14.2 UART Operations

The UART has two modes of operation, NRZ and IrDA,

which represent data in different ways for serial

communication protocols, RS-232 and IrDA.

14.2.1 NRZ mode

The non-return to zero (NRZ) mode is primarily associated

with RS-232. Each character is transmitted as a frame

delimited by a start bit at the beginning and a stop bit at the

end. Data bits are transmitted least significant bit (LSB) first,

and each bit occupies a period of time equal to 1 full bit. If

parity is used, the parity bit is transmitted after the most

significant bit. Data settings including data length, stop bit

number and parity are controlled by bit fields in UCTR.

FIGURE 14-2 illustrates a character “S” in NRZ mode.

FIGURE 14-2 NRZ ASCII “S” with Odd Parity

14.2.2 IrDA mode

IrDA mode uses character frames as NRZ mode does, but,

instead of driving ones and zeros for a full bit-time period,

zeros are transmitted as three-sixteenth (or less) bit-time

pulses (which is selected by PW[1:0] (IRCTR[2:1]), and

ones remain low. The polarity of transmitted pulses and

expected receive pulses can be inverted so that a direct

connection can be made to external IrDA transceiver

modules that use active low pulses. This is controlled by

RXINV

and TXINV (IRCTR[7:6]). IrDA mode is enabled by

control bit IREN (IRCTR[0]). FIGURE 14-3 illustrates a

character “S’ in IrDA mode.

FIGURE 14-3 IrDA ASCII “S” with Odd Parity

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