Specifications

Remote Control and Receiver-Transceiver Specifications and Requirements
for Windows Media Center in Windows Operating Systems
61
It is important to recognize that your hardware does not need to send RLC to the software
decoders in this exact form. There is a piece of software between your hardware and the
software decoders that can convert the IR from some hardware-specific form into RLC. This
software is called the ―Port Driver‖.
Port Driver/Class Driver Model
Windows Vista and Windows 7 supports the concept of an IR Port Driver/Class Driver model. In
this model, there are two drivers installed in the PC. One is a class driver, which is provided by
Microsoft. The class driver, called circlass.sys, can communicate with port drivers, and can also
decode IR protocols. The port driver is typically provided by the hardware manufacturer, and can
communicate to the hardware and send the IR information, in RLC form, up to the class driver.
IR Emitting
In addition to receiving IR, Windows Media Center must also transmit IR. IR is used to control
cable boxes and satellite boxes, which are referred to collectively as set-top boxes (STBs).
Essentially, the Windows Media Center PC acts like a cable-box remote control and transmits the
IR necessary to control the cable box. This is needed to record TV shows when the user is not
present, and to change the channel on the cable box if the user is using Extender for Windows
Media Center technology for another room.
The terms ―IR Blasting‖. ―IR Emitting‖, ―Transmitting IR‖, and ―Sending IR‖ are all used to
describe this process. These terms are synonymous.
IR Database
An IR database is stored within the Windows Media Center PC, which can be used to control an
extensive list of set-top boxes (STBs). For each STB manufacturer there is a list of IR codesets
that is unique to them. These are generally stored as RLC so Windows Media Center transmits
this information to control the STBs.
IR Learning and Parse-and-Match
IR Blasting, Learning, and Parse-and-Match must use the Windows Media Center IR Database.
Windows Media Center is unable to take advantage of any other IR databases, particularly those
stored inside of existing IR hardware solutions.
To control STBs, Windows Media Center must know which IR codes to transmit. There are three
ways that Windows Media Center can discover which codes to transmit:
 Choose from a list. The user has the option to choose a manufacturer and code set number
from amongst the IR database provided. This is very error prone because, a brand of STB might
use 5 different IR code sets depending on the STB model. The user would have to select the
manufacturer, and then manually try each of the 5 code sets until they found one that worked.
 Parse-and-Match. With the remote control, the user can use Parse-and-Match to identify the
codeset. Windows Media Center prompts the user to press a key on the remote control, for
instance the ―zero‖ button. Windows Media Center receives the RLC for the IR from the IR
hardware and compares it to all the codesets in the entire database. When Windows Media
Center finds a matching codeset, it uses that codeset to control the cable box. This allows the
user to find the correct codeset without the overhead of trying each codeset until a working set is
found. Typically, Parse-and-Match should find the users‘s codeset with 1-3 keypresses.