Re: userport: C64, Plus4, others?

From: Gerrit Heitsch <>
Date: Wed, 07 Mar 2012 18:23:35 +0100
Message-ID: <>
On 03/07/2012 10:10 AM, Gábor Lénárt wrote:

> For C64 as far as I can guess, an unrolled LDA/STA sequence can cause
> something like 7 cycles (for LDA/STA), so on 1MHz it should be
> around 140kbyte/sec. Maybe the double with C128 in 2MHz mode (can run CIAs
> in C128 with 2MHz clock?).

The CIAs in a C128 are 1MHz models and as far as I understand it, even 
if the CPU runs at 2MHz, the CIAs still run at 1MHz and the CPU clock is 
'stretched' to a 1MHz cycle if a CIA (and SID?) access is detected.

So running the C128 at 2MHz will make the copy loop faster, but not 
quite twice as fast.


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Received on 2012-03-07 18:00:24

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