Datasheet

Detailed Controller Description
10
SLLS519H—January 2010TUSB3410, TUSB3410I
3.5.1 RS-232 Data Mode
The default mode is called the RS-232 mode and is typically used for full duplex communication on SOUT and
SIN. In this mode, the modem control outputs (RTS
and DTR) communicate to a modem or are general
outputs. The modem control inputs (CTS
, DSR, DCD, and RI/CP) communicate to a modem or are general
inputs. Alternatively, RTS
and CTS (or DTR and DSR) can throttle the data flow on SOUT and SIN to prevent
receive FIFO overruns. Finally, software flow control via Xoff/Xon characters can be used for the same
purpose.
This mode represents the most general-purpose applications, and the other modes are subsets of this mode.
3.5.2 RS-485 Data Mode
The RS-485 mode is very similar to the RS-232 mode in that the SOUT and SIN formats remain the same.
Since RS-485 is a bus architecture, it is inherently a single duplex communication system. The TUSB3410
in RS-485 mode controls the RTS
and DTR signals such that either can enable an RS-485 driver or RS-485
receiver. When in RS-485 mode, the enable signals for transmitting are automatically asserted whenever the
DMA is set up for outbound data. The receiver can be left enabled while the driver is enabled to allow an echo
if desired, but when receive data is expected, the driver must be disabled. Note that this precludes use of
hardware flow control, since this is a half-duplex operation, it would not be effective. Software flow control is
supported, but may be of limited value.
The RS-485 mode is enabled by setting bit 7 (485E) in the FCRL register (see Section 7.1.4), and bit 1 (RCVE)
in the MCR register (see Section 7.1.6) allows the receiver to eavesdrop while in the RS-485 mode.
3.5.3 IrDA Data Mode
The IrDA mode encodes SOUT and decodes SIN in the manner prescribed by the IrDA standard, up to
115.2 kbps. Connection to an external IrDA transceiver is required. Communications is usually full duplex.
Generally, in an IrDA system, only the SOUT and SIN paths are connected so hardware flow control is usually
not an option. Software flow control is supported.
The IrDA mode is enabled by setting bit 6 (IREN) in the USBCTL register (see Section 5.4).
The IR encoder and decoder circuitry work with the UART to change the serial bit stream into a series of pulses
and back again. For every zero bit in the outbound serial stream, the encoder sends a low-to-high-to-low pulse
with the duration of 3/16 of a bit frame at the middle of the bit time. For every one bit in the serial stream, the
output remains low for the entire bit time.
The decoding process consists of receiving the signal from the IrDA receiver and converting it into a series
of zeroes and ones. As the converse to the encoder, the decoder converts a pulse to a zero bit and the lack
of a pulse to a one bit.