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8 536EX Chipset Developer’s Manual
Intel Confidential
Introduction
1.1.2 Windows 95 and Windows 98
When the controllerless modem chipsets are used with Microsoft Windows 95 and Windows 98
applications, the traditional UART and serial port emulations are replaced by the proprietary HaM
Mini Port driver (see Figure 2). Instead of transferring commands to UART virtual registers, then
to a serial port, the HaM Port Driver sends commands directly to the Windows virtual machine
driver VCOMM.VxD. This low-level communication driver supports the Win16 and Win32
Communication APIs. Like the WDM drivers, the Mini Port VxD drivers are fully plug and play
and conform to Microsoft WHQL certification requirements.
Figure 1. WDM Driver Block Diagram
WDM driver
Intels51.sys
Kernel - ring0
Modem drivers stack
Hardware
PCI bus
User
applications
User applications
virtual COM
port,
channel
protocols
layer