To register a license for Keil C51, two components are needed - a CID (Computer ID) and PSN (Product Serial #). The CID is different from computer to computer, so you cannot simply copy the license information from one computer to another.

        If a computer cannot access the Internet, we can obtain its PSN/CID and register it with another computer that can access the Internet. The CID and PSN can be obtained in one of the following ways:

1. If Keil uVision is installed, the CID can be seen on the registration page under [File] > [License Management]. For details, see AN104: http://www.silabs.com/Support%20Documents/TechnicalDocs/an104.pdf
    
2. To get the PSN, fill out the form on this page: http://pages.silabs.com/lp-keil-pk51.html
    
3.  If Studio is installed, you can obtain both the CID and PSN. In Studio, select [Help] > [Licensing] > [Keil 8051 ...] then click "this form" to start the registration page. Then, in the browser's address bar and in the fields of the form, you can see both the PSN and CID.

With both the PSN and CID, register for a license here: https://www.keil.com/license/install.htm. The license (LIC) can be installed under Studio, back in the Licensing Helper ([Help] > [Licensing] > [Keil 8051 ...]), or in Keil uVision under [File] > [License Management].

Chip Level Design Considerations

Optimizing System EMC Performance

Electromagnetic compatibility (EMC) optimization is a core competence of Silicon Labs. As well as implementing chip-level circuits to improve performance in a system, we have a very strong understanding of board-level design to ensure best-in-class EMC performance. We have helped many customers optimize PCBs to meet emissions standards and use our EMC lab to help solve our customers' board-level emissions problems.

Optimizing Chip-Level EMC Performance

EMC determines the ability of a product like MCU to coexist in its intended electromagnetic environment without causing or suffering functional degradation or damage to itself or to other devices that may reside in that environment – it neither is susceptible to nor causes Electromagnetic Interference (EMI). Since EMC involves the presence of a source of electromagnetic radiation, a receptor of that electromagnetic radiation and a path for that electromagnetic radiation, it is only necessary to remove two of these to achieve acceptable EMC. In general, it is not practical to completely eliminate electromagnetic radiation from a digital integrated circuit. However, by incorporating many fundamental techniques to control electromagnetic emissions from an integrated circuit and to then incorporate new methodology to reduce “leakage” of these emissions outside of the chip. From the overall system point of view, it is always more cost effective to design a product with suppression at the integrated circuit level as opposed to addressing these issues at the PCB or system level .

System Level Considerations

By designing our MCUs with EMC optimization in mind, Silicon Labs delivers solutions that reduce system level noise and interference. The following resources will enable designers to better understand system level considerations to reduce EMI, how to measure it and how to ‘design-it-out', of your PCB designs.

EMI Design Resources

• Silicon Labs EMI Tutorial
• C8051F120 Low-EMI Board
• C8051F120 Low-EMI PCB Test Results
• C8051F930-TB EMI Report
• Low-Voltage/Low-Power Products

World-Class EMC Testing Capabilities

Most electronic products require radiated EMI testing to ensure that they don't interfere with other RF systems, such as television and radio broadcast and cell phones. After meeting the required standards, an endorsement from a calibrated and certified EMI test house is issued. A TEM cell allows companies like Silicon Labs (who are in the semiconductor or product business, not the EMI testing business) do "pre-compliance" testing before going to a certified test house. The TEM cell along with an EMI receiver or spectrum analyzer comprise a system capable of making calibrated radiated field strength measurements. The TEM cell acts as a calibrated antenna and shielded enclosure, which both captures the radiated energy and blocks outside signals from the measurement. The spectrum analyzer is the receiver, which, with custom software, measures and displays the frequencies emitted and their strengths.