View source for MOS Technology 6509

The '''MOS Technology 6509''', an enhanced version of the popular [[MOS Technology 6502|6502]] [[microprocessor]], is capable of addressing up to 1 [[megabyte]] of [[random-access memory|RAM]] via [[bank switching]]. While numerous 6502-based processors can perform bank switching, they achieve this via separate logic. The 6509 has this logic on-[[integrated circuit|chip]].

Passing data between different banks requires use of the register at $1 which selects the banks to be read from and written to via LDA (zero page), Y and STA (zero page), Y CPU opcodes. The register at $0 selects the bank where the CPU fetches instructions from, which will default to 15 ($F) on power up.

The 6509 has a reputation for being difficult to program, due to its bank switching scheme. It is used in the [[Commodore CBM-II]] line of computers.

==References==
{{Reflist}}

==Further reading==
{{See also|MOS Technology 6502#Further reading|l1=List of books about 65xx microprocessor families}}

==External links==
*[http://www.devili.iki.fi/pub/Commodore/docs/datasheets/CSG/6509-8610.zip MOS 6509 datasheet (GIF format, zipped)]
*[http://archive.6502.org/datasheets/mos_6509_mpu.pdf MOS 6509 datasheet (PDF format)]

{{MOS CPU}}

[[Category:65xx microprocessors]]
[[Category:MOS Technology microprocessors]]
[[Category:8-bit microprocessors]]


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