Intel 536EX manual Parallel Host Interface 16C450/16C550A, Uart, Intel Confidential

Parallel Host Interface 16C450/16C550A UART

Parallel Host Interface 16C450/16C550A

UART 9

9.1UART 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).

Figure 11. UART Emulation in Intelsdb.VxD

MS-DOSAPPLICATION

Intelsdb.VXD

WINDOWS APPLICATION

UART EMULATION

HAM PORT DRIVER

VCOMM.VXD

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

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