Introduction; Features - Motorola DragonBall MC9328MX1 Reference Manual

Chapter 27
Universal Asynchronous Receiver/Transmitters
(UART) Modules

27.1 Introduction

This chapter describes the two universal asynchronous receiver/transmitter (UART) modules in the
MC9328MX1. The UART modules are capable of standard RS-232 non-return-to-zero (NRZ) encoding
format and IrDA-compatible infrared modes. Each UART provides serial communication capability with
external devices through an RS-232 cable or through use of external circuitry that converts infrared signals
to electrical signals (for reception) or transforms electrical signals to signals that drive an infrared LED (for
transmission) to provide low speed IrDA compatibility to the MC9328MX1.
Both UARTs transmit and receive characters that are either 7 or 8 bits in length (program selectable). To
transmit, data is written from the peripheral data bus to a 32-byte transmitter FIFO (TxFIFO). This data is
passed to the shift register and shifted serially out on the transmitter pin (TXD). To receive, data is
received serially from the receiver pin (RXD) and stored in a 32-half-words-deep receiver FIFO (RxFIFO).
The received data is retrieved from the RxFIFO on the peripheral data bus. The RxFIFO and TxFIFO
generate maskable interrupts as well as DMA Requests when the data level in each of the FIFO reaches a
programmed threshold level.
The UARTs generate baud rates based on a configurable divisor and input clock. The UARTs also contain
configurable auto baud detection circuitry to receive 1 or 2 stop bits as well as odd, even, or no parity. The
receiver detects framing errors, idle conditions, BREAK characters, parity errors, and overrun errors.
The TXD pin is configurable for open-drain operation at the chip boundary. The UART modules use a
software interface for control of modem operations and have a serial infrared (IR) module that decodes and
encodes IrDA-compatible serial IR data.

27.2 Features

• 7 or 8 data bits
• 1 or 2 stop bits
• Programmable parity (even, odd, and no parity)
• Full 8-wire serial DCE interface
• Hardware flow control support for request to send (RTS) and clear to send (CTS) signals
• Software flow control support for data set ready (DSR), data carrier detect (DCD), and ring
indicator (RI) signals on UART 2
• Edge selectable RTS and data terminal ready (DTR) edge detect interrupts
1. UART GPIO pins must be used for DTR, DSR, DCD, and RI functions.
MOTOROLA Universal Asynchronous Receiver/Transmitters (UART) Modules
1
for modem flow control on UART 2
27-1