Re: 110V to 220V

From: Mike Naberezny <>
Date: Mon, 11 May 2015 08:41:31 -0700
Message-ID: <>
On 5/11/15 4:00 AM, Michał Pleban wrote:
> Good observation! I think the only problem will be the TOD of the
> CBM-II's will be off, I can live with that.

CBM-II machines configure the TOD clock for 50 or 60 Hz automatically.

The 50/60 Hz signal is derived from the mains power inside the switching power 
supply.  The power supply output cable has a 6-pin connector that plugs into 
the mainboard.  The 50/60 Hz signal is pin 1 on that connector.  The signal is 
inverted and then goes to a 6525 TPI's IRQ0 and a 6526 CIA's TOD.

On power up, the CBM-II KERNAL routine IOINIT waits for the 50/60 Hz signal to 
change and then increments a counter until the signal changes again.  It 
compares the count against a threshold to detect 50 or 60 Hz and then sets the 
TODIN bit in CIA 2's Control Register A ($DC0E).  If bit 7 of $DC0E is set, 50 
Hz was detected.


Mike Naberezny (

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Received on 2015-05-11 16:01:18

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