Re: Real Time Clock on Cassette Write/Sense lines

From: Gerrit Heitsch <>
Date: Sat, 11 Feb 2012 18:11:07 +0100
Message-ID: <>
On 02/11/2012 07:33 AM, 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. Obviously,
> the RTC would not work if the buttons were pushed on the player, but are
> there other concerns?

In case you built that setup, it would be worth thinking about including 
a space/socket for a 24Cxxx I2C-EEPROM. They are small (8pin DIP or 8pin 
SMD) but give you up to 256KByte (24C2048) memory. They only need +5V 
and GND besides the I2C connection so the only additional cost for quite 
a bit nonvolatile storage would be the PCB space.


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Received on 2012-02-11 18:00:10

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