Hi guys i don't understand how to wire up the memory select dip forks for the apple ii. I already have one completed row of TMS4116-15NL in row C from C3 to C10 but I'm unsure how to configure it to work. I think I currently have about 16KB of RAM so far
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The RAM jumper blocks (part of the schematic of revisions 0 through 6 of the Apple II) make it possible to use either 4K or 16K DRAM chips. In 1977, the 16K DRAM had just come out and was more expensive, so this was a kind of cost-saving hack by Woz to use older—even recycled—chips.
Later revisions removed the jumper blocks completely from the design, as only 16K DRAMs were being used then. Your 4116 are 16K chips, so you just need to set up the jumpers for 16K only.
For 16K only, each of the three blocks (D1, E1, F1) must be jumpered so that the following pins are linked: 8 to 12; 9 to 13; 10 to 14. The three blocks are always jumpered the same way as each other. This puts the RAM in row C into the first 16KB of the address space, from $0000–$3FFF, and likewise row D into $4000–$7FFF, and row E into $8000–$BFFF. No 4K DRAMs can be plugged into an Apple set up like this, even if you have less than 24 of the 16K chips available.
The instructions for setting up the jumpers are in the "Apple II Reference Manual" on page 70.
You can also use the gerber files of Memory Select 16k boards for self ordering. I've also made some for 4k, but haven't used them myself yet.
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