Desperado
Veteran Member
- Joined
- Nov 25, 2017
- Messages
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Unfortunately not.....What I want to know is, do you understand how that chip functions ?
But now must i try to change this UD2 or not??
Unfortunately not.....What I want to know is, do you understand how that chip functions ?
active low or high? Thanks!but sometimes the same is indicated with a line above the symbol (a bar) or a little sloping line (well, not quite), these all indicate that the particular signal is 'active low'
active low or high? Thanks!
Maybe bad Ud2 in this case?? Can i try to replace?
unfortunately I don't understand any of this ... it's a difficult topic and since I don't know the English language very well, everything becomes more difficult for me ... Maybe I have to think about abandoning this repairWorth then thinking about what these outputs do.
So if the CPU puts binary 1100 (decimal 12) onto UD2, pins 20 & 21 are high at 5V and thus output 12 is 'active' which means that pin 14 is at 0v ('active low' outputs remember)
Which means that SEL C is now 'active'. Note that SEL C has a bar above it to indicate its an 'active low' signal. The line then has a number 4 on it indicating we go to sheet 4 to see whats done with it.
On sheet 4 we see that it goes to pin 20 of UD6 to an input CS1 with a bar above it. CS1 means chip select and the bar means its 'active low' so when this line (SEL C) is low, chip UD6 is selected to operate
yes, true!Swapping UD2 should give you a working pin 4, but this is unlikely to fix any of your current problems. But it will rule out one very small probability.
unfortunately I don't understand any of this ... it's a difficult topic and since I don't know the English language very well, everything becomes more difficult for me ... Maybe I have to think about abandoning this repair
Yes! Now but i have a new ic but the pet is not working yetOk, maybe too much
Did you get the point that UD2 takes four lines and selects one out of 16 lines ?
I don’t understand what you are saying? Have you replaced UD2 or not?Yes! Now but i have a new ic but the pet is not working yet
Why have you suggested this? What has led you to this course of action?Can i remove Pia and Via??
Yes sure, i have new ud2 on boardI don’t understand what you are saying? Have you replaced UD2 or not?
Dave
maybe a faulty 6520 o 6522 can cause scrambled screen?Why have you suggested this? What has led you to this course of action?
Dave
So, do you now have correctly formed outputs from UD2 with the NOP generator installed?Yes sure, i have new ud2 on board
yes, also on pin 4!So, do you now have correctly formed outputs from UD2 with the NOP generator installed?
Dave