IBM and NCR used a germanium or silicon diode to short together the keyboard connector pins 1 (cathode, bar) and 2 (5-pin DIN) or 1 (anode, arrow) and 5 (6-pin mini-DIN), so the POST checks the keyboard controller to see whether the jumper is installed. Compaq used to have the shorted jumper cause the POST to jump to another ROM at E000 just after power-on, which could have diagnostic code in it. It usually forces a reset, so the POST has to start from the beginning every time. The phrase Check for Manufacturing Jumper in the tables refers to one on the motherboard that makes the POST run in a continuous loop, so you can burn in a system, or use repetitive cycling to monitor a failing area with an oscilloscope or logic analyzer. The path between the CPU and the BIOS ROM, as well as basic control signals, has to be working before the POST gets to its first diagnostic test (usually the CPU register test), so some of the circuitry that the CPU test is supposed to check will be checked by the shutdown handling instead, and you will get no POST indication if a critical failure occurs. One of the problems with shutdown handling is that the POST must do some handling before anything else, immediately after power-on or system reset. Before issuing the shutdown command, the BIOS sets a value into the shutdown byte in the CMOS, which is checked after a reset, so the BIOS can branch to the relevant code and continue where it left off. The Shutdown command, on the other hand, just forces the CPU to leave protected mode for real mode, so the system behaves differently after each one. The Reset command stops the current operation and begins fetching instructions from the BIOS, as if the power has just been switched on. Consistent failures point indicate a bad battery backup system. System Initialisation involves loading configuration from the CMOS, and failures will generate a text message. Early POST failures are generally fatal and will produce a beep code, because the video will not be active in fact, the last diagnostic during Early POST is usually on the video, so that Late failures can actually be seen. The POST checks at three levels, Early, Late and System Initialisation. Having obtained a POST code, identify the manufacturer of the chipset on the motherboard, then refer to the Chipsets section to find the chip(s) that control whatever's not working. In this chapter, some general procedures are described that may help if you have no POST card. POST Diagnostic cards can read what's sent to whichever port and display the codes on a pair of numerical displays, so you can check the progress of the POST and hopefully diagnose errors when it stops, though a failure at any given location does not necessarily mean that part has the problem treat it as a guidepost for further troubleshooting (a good card is the POSTmortem™ contact the author for details, or check Useful Numbers. Those at 50h are chipset or custom platform specific. IBM PS/2s use 90, whilst some EISA machines send them to 300H as well. Some computers may use a different port, such as 84 for the Compaq, or 378 (LPT1) for Olivettis. Keep in mind that due to the unfair advantage it provides, competitive games like Call of Duty: Mobile may ban you if it detects that it’s running on an emulator.During the POST on AT-compatibles and above, special signals are output to I/O port 80H at the beginning of each test (genuine PCs and XTs don't issue POST codes, although some machines with compatible BIOSes do). Phoenix OS supports keyboard and mouse input in many popular mobile games. You can crack those fingers and start working in an Android text editor as you’ve always dreamed of, or you can try out mobile games on your new big screen. Just beware that it’s a far more cumbersome process than the executable. With them, you can even experiment installing Phoenix OS using the ISO image. The safest way to try out Phoenix OS is to install it in a virtual machine. Boot back into Windows, run the Phoenix OS executable, and select uninstall. If you decide that Phoenix OS isn’t to your taste, you can just as easily remove it. Beware that booting into it for the first time can take a while as the OS will need to optimize the local storage. Once installed, you’ll be able to select Phoenix OS as a boot option when your PC starts. Its step-by-step guide clearly directs you through the process. Installing Phoenix OS using the executable file is a straightforward process. You can create a new partition in the Windows Partition Management tool. We recommend installing Phoenix OS in a partition separate from your Windows partition.
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