User's Manual

© SENSITECH INC. CONFIDENTIAL – CONTROLLED DOCUMENT Page 36 of 83
A Carrier Corp. Company
PART NUMBER T82002163
REV A
— 1, 1½, or 2 stop-bit generation
— Baud-rate generation up to 921 kbps for all UARTs
— False start-bit detection
• 64-byte transmit FIFO
• 64-byte receive FIFO
• Complete status-reporting capability
• Ability to generate and detect line breaks
• Internal diagnostic capabilities that include:
— Loopback controls for communications-link fault isolation
— Break, parity, and framing-error simulation
• Fully prioritized interrupt system controls
• Separate DMA requests for transmit and receive data services
• Slow infrared asynchronous interface that conforms to the Infrared Data Association (IrDA)
specification
Signal Descriptions
Table 10-1 lists and describes each external signal that is connected to a UART module. The pins
transmit digital CMOS-level signals and are connected to the PXA27x processor through GPIOs.
Refer to Section 24, “General-Purpose I/O Controller” for details on the GPIOs.
Table 10-1. UARTs I/O Signal Descriptions (Sheet 1 of 2)
Name Type Description
RXD Input
Serial Input- Serial data input to the receive
shit register. In infrared mode, it is connected
to the infrared receiver input. This signal is
present on all three UARTs.
TXD Output
Serial Output—Serial data output to the communications-link 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 on all
three UARTs.
nCTS Input
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 (MSR). MSR[CTS] is the complement of the
nCTS signal. MSR[DCTS] indicates whether the nCTS input has changed state since the
last time MSR was read. nCTS has no effect on the transmitter. This signal is present on
the FFUART and BTUART. When MSR[CTS] changes state and the modem-status
interrupt is enabled, an interrupt is generated. Non-Auto-Flow Mode—When not in auto-
flow mode, MSR[CTS] indicates the state of nCTS. MSR[DCTS] indicates whether the
nCTS input has changed state since the previous reading of MSR. nCTS has no effect on
the transmitter. The user can program the UART to interrupt the processor when DCTS
changes state. Software can then stall the outgoing data stream by starving the transmit
FIFO or disabling the UART with the IER register. NOTE: If UART transmission is
stalled by disabling the UART, no MSR interrupt is received when nCTS reasserts,
because disabling the UART also disables interrupts. To get around this, either use auto-
CTS in auto-flow mode or program the nCTS GPIO pin to interrupt. Auto-Flow Mode—
In this mode, the UART transmit circuity checks the state of nCTS before transmitting
each byte. IF nCTS is high, no data is transmitted.