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  • The MOS Technology 8502 was an 8-bit microprocessor designed by MOS Technology and used in the Commodore 128. Based on the MOS 6510 that was used in the Commodore 64, the 8502 added the ability to optionally run at double clock rate of Commodore 64 with some limitations. Since the 40-column VIC-II display chip could not "steal" sufficient cycles when the CPU ran at double speed, video display in fast mode was available only with the 80-column VDC. Some 40-column applications selectively disabled the screen when performing CPU-intensive calculations so that the additional speed could be utilized when the loss of video output was unimportant. A smaller speed gain, about 35%, was also possible while keeping the 40-column display active, by switching to 2 MHz only while the VIC-II is drawing the vertical screen border, since no RAM access by the VIC is needed during that time. The pinout is a little bit different from the 6510. The 8502 has an extra I/O-pin and lacks the ϕ2-pin that the 6510 had. In 2007, HP released the HP 35s, a calculator that uses the Sunplus Technology 8502 microprocessor. This processor is not related to the MOS8502. Wikipedia