Re: Help with SX64 User Port?

From: Daniel V. Mackey <>
Date: Mon, 12 Oct 2015 21:20:20 -0400
Message-Id: <>
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?

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.


QUOTE : "A Clean bench is a sign of a weak mind."

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Received on 2015-10-13 02:01:04

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