Re: RS-232 on VIC-20

From: Jim Brain (
Date: 2004-06-21 20:52:29

Christian Johansson wrote:

>----- Original Message ----- 
>From: "MagerValp" <>
>To: <>
>Sent: Monday, June 21, 2004 7:13 PM
>Subject: Re: RS-232 on VIC-20
>>>>>>>"CJ" == Christian Johansson <> writes:
>>CJ> Has anybody been able to use the Hug RS-232 routines to get 4800
>>CJ> bps on the C128? I think it should be possible since if it is
>>CJ> possible to achieve 2400 bps on the C64 in 1 MHz with the
>>CJ> routines, it should also be possible to achieve 4800 bps on the
>>CJ> C128 in 2 MHz
>>Well, actually, the biggest problem is badlines - and they're 40 us
>>long even in 2 MHz mode. In 80 column mode with the VIC screen closed
>>it's possible to use 9600 bps though.
>I'm not very familiar with badlines. Does that problem exist even if I blank
>the screen in 40-column mode? Of course, I blank the screen when using the
>40-column mode with 2 MHz because there is not much point in seeing a lot of
>garbage moving across the screen. Anyway, I have tested that it is only
>possible to achieve 2400 bps with the built-in Kernal routines in 2 MHz mode
>and 80-column mode but I know that it is possible to achieve 9600 bps using
>custom routines (and 115200 bps if you stop using interrupts and use code
>like in Over5). What I want to know is if the Hug routine I posted in my
>previous email could perhaps be used to get at least 4800 bps by making some
>small modifications to it. I think it should be enough to change the
>definitions of the bit times but as I wrote I don't understand how they have
>been calculated.
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It should be possible, as 4800 bps leaves about 280us per bit.  However, 
I think the Hug routines reload the counter at each IRQ.  If multiple 
badlines occur per byte, then it is possible the sync could be lost.  I 
forget how many badlines there are in a second ( I would assume 25 * 
60..., which means 3-4 badlines per byte...)  but if there are more than 
3, there might be problems, as I think the Hug routines sample mid bit 
time (as in, in the middle of the period when the bit should be valid). 


Jim Brain, Brain Innovations                      
Dabbling in WWW, Embedded Systems, Old CBM computers, and Good Times!

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