Editing MSX (section)

===Keyboard===
The keyboard is a functionally separate unit which could be connected by non-multiplexed and [[Multiplexing|multiplexed]] interfaces. Multiplexed keyboard units feature additional data direction line, allowing sending scan line number to the keyboard using same data lines used for return scan code, decreasing overall number of wires between keyboard and machine. Non-multiplexed interface is usually used for internal keyboards (and some external keyboards, like Panasonic CF-3300); multiplexed interface is used for external keyboards (e.g. in Yamaha YIS805 model).

The keyboard is organized as a [[Keyboard matrix circuit|matrix]] with maximum 11 input lines and 8 output lines, accounting for maximum 88 keys (including all control, numerical and alphanumerical keys). Each scan line is regularly queried to identify the state of the keys on the line; query speed is identified by the system interrupt frequency. Such organization allows system to sense state of each key, not exhibiting notorious problem with 8042 [[microcontroller]]-based keyboards when pressing several keys simultaneously (usually more than 3) generates wrong input characters, or renders inability to sense the press of more keys.

Due to the keyboard scan being controlled by the system interrupts, one of the troubleshooting hints when an MSX machine does not display any image (assuming power is present) is to press the CAPS key to see if the respective LED toggles. If it does not toggle, the system is likely suffering a more serious problem than just lack of image on the screen (i.e. the problem with video cable or video display interface in overall).

In 2009, Kamil Karimov designed the adapter board<ref>{{Cite web |last=Karimov |first=Kamil |date=2010-02-14 |title=Контроллер PS/2 клавиатуры для MSX (Russian) |url=http://www.msx.org/node/35495?page=2#comment-187005 |url-status=live |archive-url=https://web.archive.org/web/20161222153606/https://www.msx.org/node/35495?page=2#comment-187005 |archive-date=December 22, 2016 |access-date=2013-09-20 |publisher=MSX Resource Center}}</ref> to connect a PS/2 keyboard to the multiplexed MSX keyboard interface. The firmware embedded into its [[Atmel AVR|ATTiny]] chip was tailored for Daewoo CPC machines.

In 2011, AGE Labs embedded a PS/2 keyboard controller unit, based on [[Microchip]] microcontroller, into its [[GR8BIT]] do-it-yourself machine. Its firmware is developed to directly convert PS/2 scan codes to the MSX keyboard scan codes. Thus it is fully transparent to the applications, allowing use of the controller unit with different MSX-compatible machines and for different localization setups.<ref name="language-pack" />