Re: Real Time Clock on Cassette Write/Sense lines

From: Jim Brain <>
Date: Sat, 11 Feb 2012 11:02:16 -0600
Message-ID: <>
On 2/11/2012 2:29 AM, Baltissen, GJPAA (Ruud) wrote:
> Hallo Jim,
>> But, I was afraid such constant cycling of the MOTOR line
>> with a datasette present might cause it's own issues.
> - The older CBMs have two cassette ports with each their own motor line,
> so no problem here.
> - How many people use still their cassette recorder (CR)? Unplugging the
> RTC for those rare moments they use it shouldn't be a problem, IMHO.
I would tend to agree, but I am trying to be as compatible as possible.
> - But for those people which use it regurlary, make a RTC with an edge
> connector to plug the CR in and add a switch to disable the motor line
> for the time you don't need the CR. Disadvantage: more expensive.
Well, if I use WRITE and SENSE, I don't need the switch (except on 264 
series).  Yes, I have a passthrough, but it's a passive passthrough, I 
simply pass WRITE to the RTC SCK line, and hooked SDA to the SENSE line.
> - Even a step further: make a pcb for inside the C=. First advantage:
> you can directly tap the motor signal at TTL level. And. if needed, let
> the owner add a switch to disable the motor line. This can be done by
> desoldering one pin of the transistor and wire the pin and the hole to a
> switch. Advantages: even less expensive (no connector(s) needed) and no
> removal needed during transport. One can even use a bigger (rechargeble)
> battery.

If I went to all of the trouble to do something inside, there are SO 
many other and better options for hooking this thing into the memory 
map.  I know I'm mentioning this to the wrong crowd, but the majority of 
people who still own these units would rather do anything than open up 
their 30+ year old machine.

Full disclosure:  Many products require a source of 5VDC from the 
machine, and the cassette port is an ideal location.  Such pigtails 
requires a small PCB to create the passthrough portion.  When I 
initially designed the cassette passthrough PCB, it bothered me that it 
was mainly a waste of PCB space.  So, extended it just a tiny bit, 
mainly to make it easier to grab onto for removal, and added a DIP14 
footprint matching a ATTINY24/44/84 uC, a simple voltage divider for the 
motor line, and some jumpers for READ/WRITE/SENSE.  I didn't have any 
expectations for use, but it seemed better than leaving the PCB plain.  
Now, I need to make a new order, and thought I might add an RTC, because 
it's a simpler idea (no uC programming needed, just install an RTC and 
write some 6502 code).  It's a through-hole design, and parts can be 
sourced easily, so I thought it would make a neat DIY project.  Anyway, 
that's why it's external.


Jim Brain

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Received on 2012-02-11 18:00:03

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