Intel PXA255 manual Uart Signal Descriptions Sheet 1, Name Type Description, Rxd, Txd

Models: PXA255

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UARTs

10.3Signal Descriptions

Table 10-1lists and describes each external signal that is connected to a UART module. The pins are connected through the System Integration Unit to GPIOs. Refer to Section 4.1, “General- Purpose I/O” on page 4-1for details on the GPIOs.

Table 10-1. UART Signal Descriptions (Sheet 1 of 2)

Name

Type

Description

 

 

 

 

 

SERIAL INPUT: Serial data input to the receive shift register. In infrared

RXD

Input

mode, it is connected to the infrared receiver input. This signal is present on

 

 

all three UARTs.

 

 

 

 

 

SERIAL OUTPUT: Serial data output to the communications link-

TXD

Output

peripheral, modem, or data set. The TXD signal is set to the logic 1 state

upon a Reset operation. It is connected to the output of the infrared

 

 

 

 

transmitter in infrared mode. This signal is present all three UARTs.

 

 

 

 

 

CLEAR TO SEND: When low, indicates that the modem or data set is ready

 

 

to exchange data. The nCTS signal is a modem status input and its

 

 

condition can be tested by reading bit 4 (CTS) of the Modem Status

 

 

Register. Bit 4 is the complement of the nCTS signal. Bit 0 (DCTS) of the

nCTS

Input

Modem Status Register (MSR) indicates whether the nCTS input has

changed state since the last time the Modem Status Register was read.

 

 

nCTS has no effect on the transmitter. This signal is present on the

 

 

FFUART and BTUART.

 

 

When the CTS bit of the MSR changes state and the Modem Status

 

 

interrupt is enabled, an interrupt is generated.

 

 

 

 

 

DATA SET READY: When low, indicates that the modem or data set is

 

 

ready to establish a communications link with a UART. The nDSR signal is

 

 

a Modem Status input and its condition can be tested by reading Bit 5

nDSR

Input

(DSR) of the MSR. Bit 5 is the complement of the nDSR signal. Bit 1

(DDSR) of the MSR indicates whether the nDSR input has changed state

 

 

since the MSR was last read. This signal is only present on the FFUART.

 

 

When the DSR bit of the MSR changes state, an interrupt is generated if the

 

 

Modem Status interrupt is enabled.

 

 

 

 

 

DATA CARRIER DETECT: When low, indicates that the data carrier has

 

 

been detected by the modem or data set. The nDCD signal is a modem

 

 

status input and its condition can be tested by reading Bit 7 (DCD) of the

 

 

MSR. Bit 7 is the complement of the nDCD signal. Bit 3 (DDCD) of the MSR

nDCD

Input

indicates whether the nDCD input has changed state since the previous

 

 

reading of the Modem Status Register. nDCD has no effect on the receiver.

 

 

This signal is only present on the FFUART.

 

 

When the DCD bit changes state and the Modem Status interrupt is

 

 

enabled, an interrupt is generated.

 

 

 

Intel® PXA255 Processor Developer’s Manual

10-3

Page 361
Image 361
Intel PXA255 manual Uart Signal Descriptions Sheet 1, Name Type Description, Rxd, Txd