Hardware UART

17

This chapter describes the signal definitions and operations of the PXA255 processor hardware UART (HWUART) port.

The HWUART interface pins are available via either the PCMCIA general purpose I/O (GPIO) pins or the BTUART pins. Refer to Section 4.1.2, “GPIO Alternate Functions” for more information. When using the HWUART through the PCMCIA pins, they are driven at the same voltage level as the memory interface. Because the PCMCIA signal nPWE is used for variable- latency input / output (VLIO), VLIO cannot be used while the HWUART interface is using the PCMCIA pins.

The HWUART is configured differently than the other UARTs. The HWUART supports full hardware flow control.

17.1Overview

The HWUART contains a UART and a slow infrared transmit encoder and receive decoder that conforms to the IrDA Serial Infrared (SIR) Physical Layer Link Specification.

The UART performs serial-to-parallel conversion on data characters received from a peripheral device or a modem and parallel-to-serial conversion on data characters received from the processor. The processor can read the UART’s complete status during functional operation. Status information includes the type and condition of transfer operations and error conditions (parity, overrun, framing, or break interrupt) associated with the UART.

The HWUART operates in FIFO or non-FIFO mode. In FIFO mode, a 64-byte transmit FIFO holds data from the processor until it is transmitted on the serial link and a 64-byte receive FIFO buffers data from the serial link until it is read by the processor. In non-FIFO mode, the transmit and receive FIFOs are bypassed.

The HWUART can also use direct memory access (DMA) to transfer data to and from the

HWUART.

17.2Features

Software can program interrupts to meet its requirements. This minimizes the number of computations required to handle the communications link. The UART operates in an environment that is controlled by software and can be polled or is interrupt driven. The HWUART has these features:

Functionally compatible with the 16550A and 16750 UART specifications. The UART supports not only the 16550A and 16750 industry standards but these additional functions as well:

DMA requests for transmit and receive data services

Slow infrared asynchronous interface

Intel® PXA255 Processor Developer’s Manual

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Intel PXA255 manual Hardware Uart