Re: Help with SX64 User Port?

From: Leif Bloomquist <>
Date: Mon, 12 Oct 2015 21:25:28 -0400
Message-ID: <>
Thanks, I know about the mod  (link is, I believe).

I'd hate to have to ask users to mod their SX, especially since an
EZ232 works on a stock SX64.


On Mon, Oct 12, 2015 at 9:20 PM, Daniel V. Mackey <> wrote:
> At 09:09 PM 10/12/2015, you wrote:
>> Hi all,
>> Some of you know I've been tinkering with an Arduino-based Wifi
>> "Modem" for the Commodore 64 etc.  (Pics here:
>> It's almost ready to go, however, one issue is that it doesn't work on
>> the SX64, and it's the same issue on at least two SX's.
>> The symptom is that while the Arduino receives serial data from the SX
>> fine, nothing sent by the Arduino is received by the SX.   I've also
>> tried going directly to the Wifi board (which is also serial), same
>> issue.   It works fine on a normal 64/64C though.
>> I'm aware that there are some differences with the SX User Port
>> compared to a normal 64/64C  (one of the 9VAC lines is "grounded",
>> from what I've read).  I don't have a lot of electronics background so
>> I could really use some help.
>> An EZ232 works just fine on my SX, so it's clearly possible.  This is
>> all at 2400 baud.
>> Some theories I have:
>> -I tied all the grounds (both signal and protective ground) on the
>> user port together on my board, could there be an issue from the 9VAC
>> coming through the ground?   (I'm not using the 9VAC pins themselves,
>> they aren't even connected.)
>> -I'm going through 330 ohm resistors to protect the CIA  (i.e. in case
>> User port and Arduino pins are both outputs).  Could this be putting
>> the TTL signal out of spec on the SX, but not on the 64(C)?
>> I'll post a schematic momentarily, but wanted to ask if anyone has
>> some advice or info as to what the problem might be?
>> Thanks
>> -Leif
> Hey Schema,
> There is a MOD for the expansion port. I can't for the life of me find the
> link at the moment, maybe someone else
> can find it. I DID do the mod on my SX when I had it apart awhile back.
> ---
> WWW:
> QUOTE : "A Clean bench is a sign of a weak mind."
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Received on 2015-10-13 02:02:14

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