Re: strange read with a 6502...

From: didier derny <didier_at_aida.org>
Date: Thu, 31 Mar 2016 21:55:26 +0200
Message-ID: <56FD80AE.3090402@aida.org>
cs is low for the entire phi2 cycle
phi2 in  blue, cs in red

cs is build from a cs from the bus subdivided by a 74ls138 + 74ls04



On 31/03/2016 21:45, Gerrit Heitsch wrote:
> On 03/31/2016 09:35 PM, didier derny wrote:
>> Finally it works at even and odd addresses
>>
>> I observed both case with the oscilloscope  ODD and EVEN addresses
>>
>> the differences between both case was  that when the code was at odd
>> addresses
>> the A0 line was at the same value for the next cycle,
>> so the hypothesis was that CH376 was removing the data to fast when A0
>> changed...
>>
>> so I added a small capacitor between A0 and GND  (on the CH376)
>>
>> now A0 is delayed and it works where ever is the code (odd/even)
>>
>> how  could I solve this problem properly ?
>> I don't like this capacitor on the address bus...
>
> You still didn't tell us if CS is low while PHI2 is high or not. 
> Mixing this up would explain your problem...
>
>  Gerrit
>
>
>
>
>>
>> thanks to all
>>
>> -- 
>> didier
>>
>>
>> On 30/03/2016 22:08, Gerrit Heitsch wrote:
>>> On 03/30/2016 09:44 PM, didier derny wrote:
>>>> if I remove the board and inject a signal on A0
>>>> I get the signals on other pins   a few mv
>>>> a little bit higher on CS
>>>>
>>>> I checked with the oscilloscope
>>>>
>>>> CS / PHI2  with the code odd/even seems ok   cs go low on falling edge
>>>> of phi2  / go up on raising edge of phi2  (same for odd and even)
>>>
>>> Huh? According to what I could find, CS is low_active on that chip.
>>> Meaning you need to have CS low when PHI2 is high.
>>>
>>>  Gerrit
>>>
>>>
>>>
>>>       Message was sent through the cbm-hackers mailing list
>>
>>
>>        Message was sent through the cbm-hackers mailing list
>>
>>
>
>
>       Message was sent through the cbm-hackers mailing list



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Received on 2016-03-31 20:00:51

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