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|''Bit''||''Description''||''Usagein CPC''||Usage in KC Compact
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|7||CAS.IN||Cassette read dataRdata input||Cassette data input
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|6||PRN.BUSY||Parallel/Printer port ready signal||"1" = not ready, "0" = Ready
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|5||/EXP||(note 6)||Expansion Port /EXP pin||Printer data bit7
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|4||LK4(note 5)||Screen Refresh Rate||Purpose unknown (set to "1")
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|3||LK3(note 1)||Manufacturer ID||Purpose unknown (note 4set to "1")
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|2||LK2(note 2)||Manufacturer ID||Purpose unknown (set to "0")
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|1||LK1(note 3)||Manufacturer ID||Expansion Port /TEST pin
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|0||6845 VSYNC||State of VSYNC from 6845. "1" = VSYNC active, "0" = VSYNC inactive
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