stm32 usb虚拟两路串口，下面这个pc端的驱动，有个MI_00和MI_02是指什么？

usb虚拟两路串口，下面这个pc端的驱动，有个MI_00和MI_02是指什么？

; STMicroelectronics Comunication Device Class driver instalation file
; (C)2006 Copyright STMicroelectronics
;

[Version]
Signature="$Windows NT$"
Class=Ports
ClassGuid={4D36E978-E325-11CE-BFC1-08002BE10318}
Provider=%STM%
LayoutFile=layout.inf
DriverVer=10/02/06

[Manufacturer]
%STM%=DeviceList

[DestinationDirs]
DefaultDestDir=12

[SourceDisksFiles]

[SourceDisksNames]

[DeviceList]
"STM32 USART Port A"=STMUSB, USBVID_03EB PID_6133 MI_00
"Stm32 USART Port B"=STMUSB, USBVID_03EB PID_6133 MI_02
"Stm32 USART Port C"=STMUSB, USBVID_03EB PID_6133 MI_04
;------------------------------------------------------------------------------
;  Windows 2000/XP Sections
;------------------------------------------------------------------------------

[STMUSB.nt]
include=mdmcpq.inf
CopyFiles=DriverCopyFiles
AddReg=STMUSB.nt.AddReg

[DriverCopyFiles]
usbser.sys,,,0x20

[STMUSB.nt.AddReg]
HKR,,DevLoader,,*ntkern
HKR,,NTMPDriver,,usbser.sys
HKR,,EnumPropPages32,,"MsPorts.dll,SerialPortPropPageProvider"

[STMUSB.nt.Services]
AddService=usbser, 0x00000002, DriverService


[STMUSB.nt.HW]
include=mdmcpq.inf

[DriverService]
DisplayName=%DESCRIPTION%
ServiceType=1
StartType=3
ErrorControl=1
ServiceBinary=%12%usbser.sys

;------------------------------------------------------------------------------
;  String Definitions
;------------------------------------------------------------------------------

[Strings]
STM="STMicroelectronics"
DESCRIPTION="STM32F10x DUAL CDC"