Types Of Uarts; Full Function Uart; Full Function Uart Signals; Ffuart Interface Signals - Intel PXA27 Series Design Manual

Table 10-1. UART Signal Descriptions (Sheet 2 of 2)
Name Direction
RING INDICATOR – When low, indicates the modem or data set has received a telephone ringing signal. The
nRI signal is a Modem Status input whose condition is tested by reading Bit 6 (RI) of the MSR. Bit 6 is the
complement of the nRI signal. Bit 2, the trailing edge of ring indicator (TERI), of the MSR indicates whether the
nRI input signal has changed from low to high since the MSR was last read. This signal is present only on the
nRI Input
FFUART.
When the RI bit of the MSR changes from a high to low state and the Modem Status interrupt is enabled, an
interrupt is generated.
DATA TERMINAL READY – When low, signals the modem or the data set that the UART is ready to establish
a communications link. The nDTR output signal is set to an active low by programming Bit 0 (DTR) of the MSR
nDTR Output
to a 1. A Reset operation sets this signal to its inactive state. LOOP mode operation holds this signal in its
inactive state. This signal is present only on the FFUART.
REQUEST TO SEND – When low, signals the modem or the data set that the UART is ready to exchange
data. The nRTS output signal is set to an active low by programming Bit 1 (RTS) of the Modem Control
Register to a 1. A Reset operation sets this signal to its inactive (high) state. LOOP mode operation holds this
signal in its inactive state. This signal is used by the FFUART and BTUART.
nRTS Output Non-Autoflow Mode: The nRTS output signal is asserted by setting bit 1 (RTS) of the Modem Control register
to a 1. The RTS bit is the complement of the nRTS signal.
Autoflow Mode: nRTS is automatically asserted by the autoflow circuitry when the Receive buffer exceeds its
programmed threshold. It is de-asserted when enough bytes are removed from the buffer to lower the data
level back to the threshold.
10.3

Types of UARTs

The PXA27x processor has three separate UARTs; however, each UART is different with respect
to signals and features supported. The UARTs are described in this section.
10.3.1

Full Function UART

The FFUART supports modem control capability. The maximum baud rate is 921,600 bps.
10.3.1.1

Full Function UART Signals

See Table 10-2
Table 10-2.

FFUART Interface Signals

Signal
Name
FFRXD
FFTXD
FFCTS
FFDSR
FFDCD
FFRI
FFDTR
FFRTS
®
Intel PXA27x Processor Family Design Guide
for the list and description of the Full Function UART signals.
Direction
Input Full Function UART Receive, serial data input to the UART
Output Full Function UART Transmit, serial data output from the UART
Input Full Function UART Clear to Send
Input Full Function UART Data Set Ready
Input Full Function UART Data Carrier Detect
Input Full Function UART Ring Indicator
Output Full Function UART Data Terminal Ready
Output Full Function UART Request to Send
Description
Description
UART Interfaces
II:10-3