Re: Real Time Clock on Cassette Write/Sense lines

On 2/11/2012 2:25 AM, Marko Mäkelä wrote:
> On Sat, Feb 11, 2012 at 12:33:04AM -0600, Jim Brain wrote:
>> Anyone see issues with wiring up a I2C-based (DS1307-type) RTC to the 
>> cassette port with SCK on WRITE and SDA (data) on sense?  Looking at 
>> schematics, READ is often hooked to CA1 or similar read-only pin, but 
>> SENSE appears to be on a GPIO on all CBM machines I found.
>
> Did you check all machines? IIRC, SENSE is an output-only on some 
> computer (maybe the 264 series aka C16, C116, plus/4, or the 600/700 
> series). Otherwise, I would have used SENSE in the custom protocol of 
> the C2N232.
B series uses PB7 of a 6525, which appears to be IO.  I didn't check the 
+4 series since I'll need to different connector for that anyway.
>
>> My other idea is to put SCK on MOTOR and put SDA on the WRITE line, 
>> which looks to be a GPIO.  But, I was afraid such constant cycling of 
>> the MOTOR line with a datasette present might cause it's own issues.
>
> Some fast disk copying program on the C64 (File hack'em or Fast 
> hack'em) did cycle the MOTOR line when switching memory banks. It 
> would emit a funny noise on the datassette, that's all. I guess that 
> the authors did not have a datasette hooked up.

My hope was to use this "inline", for those who want to continue to use 
the datasette (the US has largely forgotten about the datasette, but EU 
still uses it quite a bit, or so the forums appear to show).  SENSE is 
the only line that is not actively driven high by the datasette.

Jim

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