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Thread: Got a nice late Apple ][ for cheap

  1. #11

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    The function of S2 has something to do with pins 6, 7, 9 and 10 data output pins on the encoder chip. Normally, pins 9 and 10 connect to inverters (74LS04 on the encoder PCB,) which is then fed to a 74LS257 (B7 on the motherboard) The output of that chip is then fed to the DP8304 transceiver (H10.)

    What S2 does is allow switching between pairs 9/10 with pins 6/7. These two illustrations will show you how all of this is connected. But, it still doesn't explain the actual function. I checked Sather, Willegal and several other sources, and no one seems to talk about this.

    Capture.JPG Capture1.JPG

  2. #12

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    Alright! Better late then never..... Found out the function of S2 on the Apple II encoder board.

    With a SPDT switch installed, the only thing it really does is disable the SHIFT key from functioning for the "P", "N" and "M" keys. Normally, SHIFT-"N" generates the "^" character, "P" generates "@" and SHIFT-"M" generates the right "]" character. But with the S2 switch switching from pins 9/10 to 6/7 on the encoder chip, it disables these shift functions. So when I hit SHIFT and these letters, it generates the letters and not the special characters.


    IMG_3596x.jpgIMG_3597.jpgIMG_3601.jpg

    I have to wonder what purpose would this serve?

    If you want to do this to your keyboard encoder board, you first need to break the jumper pads as shown in the first photo. Get a SPDT switch, pop it in and away you go!
    Last edited by groink; August 3rd, 2019 at 11:54 PM.

  3. #13

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    Finally found an explanation of the S2 switch. I found it in the book "Apple II Circuit Description," page 93. Too much typing to repeat here. It basically says that with the AY-5-3600-931-B6 encoder, S2 allows you to utilize a feature of this particular "B6" encoder called "quad-mode," "quad" meaning the "P", "N" and "M" keys can generate up to four different characters, basically subbing bits 8/9 with 5/6. There's a lot more to it - you need to read it to get the full explanation.

    Unfortunately, my encoder is a KR3600-070. I'll have to hunt for a AY-5-3600-931-B6 to do more exploring.
    Last edited by groink; August 4th, 2019 at 12:06 AM.

  4. #14
    Join Date
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    Quote Originally Posted by groink View Post
    Finally found an explanation of the S2 switch. I found it in the book "Apple II Circuit Description," page 93. Too much typing to repeat here. It basically says that with the AY-5-3600-931-B6 encoder, S2 allows you to utilize a feature of this particular "B6" encoder called "quad-mode," "quad" meaning the "P", "N" and "M" keys can generate up to four different characters, basically subbing bits 8/9 with 5/6. There's a lot more to it - you need to read it to get the full explanation.

    Unfortunately, my encoder is a KR3600-070. I'll have to hunt for a AY-5-3600-931-B6 to do more exploring.
    I think S2 is for lower case ?

    From page 93

    "Lowercase-There are two bow ties on the board with the ICs. They may be cut
    as a user option. The circuit is then restored by adding switch S2. In the normal
    position of S2, the circuit functions as previously described. When S2 is operated,
    output bits 9 and 8 are substituted for bits 5 and 6, Encoder B6 has been programmed
    with ASCII lowercase letters"

    So when pressing a key with S2 open, bits 5 & 6 would always be 1, The comment 'bits 9 and 8 are substituted for bits 5 and 6' seems odd though, it only forces bits 5 & 6 high (well, low and inverted in B5 to high) unless the representation of switch S2 isnt perfect (it does show B8 & B9 connected into the dotted box of S2). Maybe S2 should actually select B5 or B9 to bit 5 and B6 or B8 to bit 6 but I imagine the Apple II rom would also need to be able to understand this.

    All the keys are Quad mode. Its just that the chip is only programmed with physical keys P, N & M to actually have four different output codes, look at fig C-22. Each button is divided into four, but most have duplicate quadrants, ie key 6 has two '6' and two '&' whereas P has 'P', '@', DLE and NUL.
    Last edited by Gary C; August 4th, 2019 at 12:43 AM.

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