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92 536EX Chipset Developer’s Manual
Intel Confidential
Parallel Host Interface 16C450/16C550A UART
Parallel Host Interface 16C450/16C550A
UART 9
9.1 UART Emulation in the Controllerless Modem
When controllerless modems are used with Windows applications, the communication driver
architecture eliminates the need for a UART emulation (see Section 1.1, “Controllerless Modem
Driver Overview” on page 7). However, MS-DOS applications used with controllerless modems
retain the need for a UART emulation. Therefore, Intel provides the Intelsdb.VXD driver, which
includes this UART emulation and also interacts directly with the Windows VCOMM.VxD driver
(see Figure 11).
The parallel host interface of the FastPath family emulate the electrical and register functions of a
16550A and 16C450 UART. Upon modem reset, the modem defaults to a 16C450. The host (DTE)
can then configure the UART to function as a 16C550A UART.
In 16C450 emulation mode, the DTE and modem transfer data back and forth a byte at a time. In
16C550A emulation mode, the modem provides two 16-byte FIFO buffers, one for the transmitter
and another for the receiver. Thus, up to 16 bytes of data may be sent to or received from the
Figure 11. UART Emulation in Intelsdb.VxD
MS-DOS
APPLICATION
Intelsdb.VXD
UART EMULATION
WINDOWS
APPLICATION
VCOMM.VXD
HAM PORT DRIVER