OXCFU950_07 Datasheet, PDF (39/74 Pages) Oxford Semiconductor – USB/UART multi-function 16-bit PC Card device

OXFORD SEMICONDUCTOR, INC.
OXCFU950 DATA SHEET
8 UART INTERFACE
The internal UART in the OXCFU950 is based on that used in the well-proven OX16C95x UARTs, but with a number of
significant enhancements. It is referred to throughout this document as the OXCFU950 UART core, or simply UART.
8.1 Mode Selection
The OXCFU950 UART is software-compatible with the 16C450, 16C550, 16C654 and 16C750 UARTs. The operation of the 950
depends on a number of modes which are referenced throughout this data sheet. The FIFO depth and compatibility modes are
tabulated below:
UART Mode
FIFO
FiCR[0] Enhanced mode
FiCR[5]
size
(EFR[4]=1)
(guarded with LCR[7] = 1)
450
1
0
X
X
550
16
1
0
0
650
128
1
1
X
750
128
1
0
1
950*
128
1
1
X
Table 12: UART Mode Configuration
* Note that 950 mode configuration is identical to 650 configuration
8.1.1 450 Mode
After a hardware reset, bit 0 of the FiCR is cleared, making
the 950 compatible with the 16C450. The transmitter and
receiver FIFOs (referred to as the Transmit Holding
Register and Receiver Holding Register respectively) have
a depth of one. This is referred to as byte mode. When
FiCR[0] is cleared, all other mode selection parameters are
ignored.
8.1.2 550 Mode
After a hardware reset, writing a 1 to FiCR[0] increases the
FIFO size to 16, providing compatibility with 16C550
devices.
8.1.3 750 Mode
Writing a 1 to FiCR[0] increases the FIFO size to 16. In a
similar fashion to 16C750, the FIFO size can be further
increased to 128 by writing a 1 to FiCR[5]. Note that
access to FiCR[5] is protected by LCR[7]; i.e., to set
FiCR[5], software should first set LCR[7] to remove the
guard temporarily. When FiCR[5] is set, software should
clear LCR[7] for normal operation.
The 16C750 additional features over the 16C550 are
available as long as the UART is not put into Enhanced
mode (i.e. EFR[4] should be 0). These features are:
1. Deeper FIFOs
2. Automatic RTS/CTS out-of-band flow control
8.1.4 650 Mode
The 950 is compatible with the 16C654 when EFR[4] is set,
i.e., the device is in enhanced mode. Because 650
software drivers usually put the device into enhanced
mode, running 650 drivers on the 950 results in 650
compatibility with 128-deep FIFOs, as long as FiCR[0] is
set. Note that the 650 emulation mode of the 950 provides
128-byte deep FIFOs whereas the standard 16C654 has
only 32 byte FIFOs.
650 mode has the same enhancements as the 16C750
over the 16C550, but these are enabled using different
registers.
There are also additional enhancements over those of the
16C750 in this mode, these are:
1. Automatic in-band flow control
2. Special character detection
3. Infra-red IrDA format transmit and receive mode
4. Transmit trigger levels
5. Optional clock prescaler
DS-0023 February 2007
External—Free Release
Page 39 of 74