Re: userport: C64, Plus4, others?

From: Gerrit Heitsch <>
Date: Tue, 06 Mar 2012 17:20:51 +0100
Message-ID: <>
On 03/05/2012 11:10 PM, Gábor Lénárt wrote:
> Hi,

> I prefer user port, because it exists on other machines as well, not just
> C64. Like Plus/4. And it's my another question: it's not so clear for me:
> has the Plus/4 some similar handshaking possibilities via its user port as
> the C64/CIA has?

No. The Plus/4 user port is completly different. The I/O-Bits are the 
portbits of a 6529B, one of them used to detect the button press for the 
datasette (If no tape is attached you have all 8 bits). Those are just 
I/O, no handshake other features available. You don't even have a data 
direction register. To use a bit as input, write a '1' to it before 
reading it.

The Plus/4 also has a real ACIA (8551/6551A) for the RS232. You only 
need a few inverters and a MAX232 to be able to use it with a modem or a 
PC on the other side. Without modification, you can reach 19200 bps. 
This also means you cannot easily 'abuse' those I/O bits for other purposes.


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Received on 2012-03-06 17:00:29

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