XR19L220_07 Datasheet, PDF (5/43 Pages) Exar Corporation – SINGLE CHANNEL INTEGRATED UART AND RS-232 TRANSCEIVER

XR19L220
REV. 1.0.1
SINGLE CHANNEL INTEGRATED UART AND RS-232 TRANSCEIVER
1.0 PRODUCT DESCRIPTION
The XR19L220 interface converter consists of a full-functional UART with 16 bytes of transmit and receive
FIFO, a charge pump, three RS-232 drivers, five RS-232 receivers, and a sleep/Power-Save mode circuitry. It
operates from a single +3V to 5.5V supply at 250Kbps data rate, while meeting all EIA RS-232F specifications.
Its feature set is fully compatible to the XR16L580 device. Unlike the XR16L580, the modem signals are not
CMOS/TTL level, but conform to EIA/TIA 232 or RS-232 voltage levels. The configuration registers set is
16550 UART compatible for control, status and data transfer. Also, the L220 has 16-bytes of transmit and
receive FIFOs, automatic RTS/CTS hardware flow control, automatic Xon/Xoff and special character software
flow control, transmit and receive FIFO trigger levels, and a programmable baud rate generator with a
prescaler of divide by 1 or 4. Additionally, the L220 includes the ACP pin which the user can shut down the
charge pump for the RS-232 drivers when the L220 is already in sleep mode. The Power-Save feature further
isolates the databus interface to further reduce power consumption in the sleep mode. The L220 is fabricated
using an advanced CMOS process.
Enhanced Features
The L220 UART provides a solution that supports 16 bytes of transmit and receive FIFO memory. The L220 is
designed to work with low supply voltage and high performance data communication systems that require fast
data processing time. Increased performance is realized in the L220 by the transmit and receive FIFOs, FIFO
trigger level controls and automatic flow control mechanism. This allows the external processor to handle more
networking tasks within a given time. This increases the service interval giving the external CPU additional time
for other applications and reducing the overall UART interrupt servicing time. In addition, the L220 provides the
Power-Save mode that drastically reduces the power consumption when the device is not used. The
combination of the above greatly reduces the CPU’s bandwidth requirement, increases performance, and
reduces power consumption. Finally, since the L220 includes an RS-232 transceiver and a full-modem
interface, it can be connected to an RS-232 serial cable directly.
Intel or Motorola Data Bus Interface
The L220 provides a host interface that supports Intel or Motorola microprocessor (CPU) data bus interface.
The Intel bus compatible interface allows direct interconnect to Intel compatible type of CPUs using IOR#,
IOW# and CS# inputs for data bus operation. The Motorola bus compatible interface instead uses the R/W#
and CS# signals for data bus transactions. See pin description section for details on all the control signals. The
Intel and Motorola bus interface selection is made through the pin, I/M#.
Data Rate
The L220 is capable of operation up to 250Kbps data rate using the 16X internal sampling clock rate. The
UART section can operate at much higher speeds, but the speed of the RS-232 transceiver is limited to
250Kbps beyond which the L220 cannot comply with the EIA/TIA-232 electrical characteristics. The device can
operate either with a crystal on pins XTAL1 and XTAL2, or external clock source on XTAL1 pin.
Internal Enhanced Register Sets
The L220 UART has a set of enhanced registers providing control and monitoring functions. Interrupt enable/
disable and status, FIFO enable/disable, selectable TX and RX FIFO trigger levels, automatic hardware/
software flow control enable/disable, programmable baud rates, modem interface controls and status, sleep
mode and mode are all standard features. Following a power on reset or an external reset (and operating in 16
or Intel Mode), the registers defaults to the reset condition and is compatible with the XR16L580.
RS-232 Interface
The L220 includes RS-232 drivers/receivers for the entire modem interface. This feature eliminates the need
for an external RS-232 transceiver. The charge pump provides output voltages of +5V and -5V for its drivers
over the 3.0V to 5.5V VCC supply voltage. The serial outputs TX, RTS and DTR swing between -5V (inactive)
and 5V (active) RS-232 voltage levels. The serial inputs RX, CTS, DSR, CD and RI are RS-232 receivers and
can take any voltage swing from -15V to +15V. The receivers are always active, even in Full Sleep and Power-
Save modes. The RS-232 drivers guarantee a data rate of 250Kbps even when fully loaded with 3Kohm in
parallel with 1000pF load. Also, the slew rate of the driver output is internally limited to a maximum of 30V/us in
order to meet the EIA-232F standard.
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