MCS7840
USB-2.0 to Four Serial Ports
Page 8
Rev.
1.2
UART Functional Description
Overview
The UARTs are high performance serial ports that comply with the 16c550 specification. All UARTs are similar
in operation and function, and are described in this section. The function of a single UART is described below.
Operation Modes
The UARTs are backward compatible with 16c450 and 16c550 devices. The operation of the port depends
upon the mode settings, which are described throughout the rest of this section. The modes, conditions and
corresponding FIFO depth are tabulated below.
UART Mode
FIFO Size
FCR[0]
450
1
0
550
16
1
450 Mode
After the hardware reset, bit-0 of the FIFO Control
Register (FCR) is cleared, and the UART is
compatible with the 16c450 mode of operation.
The transmitter and receiver FIFOs (referred to as
the “Transmitter Holding Register” and “Receiver
Holding Register” respectively) have a depth of
one.
This mode of operation is known as “Byte Mode”.
550 Mode
After the hardware reset, writing a 1 to FCR[0]
will increase the FIFO size to 16, providing
compatibility with 16c550 devices.
In 16c550 mode, the device has the following
features:
•
RTS/CTS hardware flow control or
DSR/D
TR hardware flow control
•
Infrared IrDA format transmit & receive
mode
•
Deeper (16-Byte) FIFOs
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