Re: 'Frankenstein' Disk Drives, Done Cheap

From: Greg King <>
Date: Tue, 29 Apr 2014 11:54:16 -0400
Message-id: <>
On 2014-04-29 2:16 AM, Gerrit Heitsch wrote:
> On 04/28/2014 11:26 PM, smf wrote:
>>> Probably running the 1571, and by extension, the CIA in it, at 2 MHz.
>>> Even when running the C128 at 2 MHz, the CIAs will still be clocked at
>>> 1 MHz.
>> I wonder why they run the CIAs in the 1571 at 2Mhz., but the C128 only
>> ever 1Mhz.
> Maybe they were not able to make enough of them that could run at 2 MHz.
> That way, they could use all CIAs for the C128.
> Also, you get timers that always run the same speed, no matter what the
> CPU is clocked at.

And, the PC handshaking line is pulsed for one system-clock cycle when 
port B is accessed.  Many devices from that time period expect those 
strobes to last at least 1 microsecond.  They can't see shorter pulses.

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Received on 2014-04-29 17:00:03

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