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Atari 2600 TIA NTSC and PAL

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Hi Everybody...


I have some questions (technical ones) about the TIA chip of the Atari 2600. Hope someone will help me...


There is a difference in the pinout of both versions (NTSC and PAL) of the TIA. Attached to this message are the pinouts:





During my investigations I found discrepancies in the pinout assignements of the CS0, CS1, CS2 and CS3 lines. The questions are:


1. what are those CSx lines for ?

2. Are the assignements in the attached files correct?

3. Why CS0,CS1 and CS3 are low bit enable and not CS2?

4. What is the !BLK line for?

5. What are the PAL-I and PAL-S lines for in the PAL version?

6. Does any one has a Field Service manual for the Atari 2600?


Thanks for any reply and any help...






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The CSX lines are the Chip Selects. To enable a read or write to the TIA, CS0, CS1 and CS3 need to be low and CS2 needs to be hi. The reason for the different polarities is to make address decoding easier, but it appers that CS2 and CS3 where never used since they are tied to a high and low respectively.


The BLK signal indicates that the video is either in the horizontal or vertical blanking period.


I am going to gues that PAL-I and PAL-S are the video clock inputs. On the NTCS machine the video frequency is derived from the main system clock, but since PAL uses a different base video frequency a second clock input is provided so that the CPU/system clock can remain the same as the NTCS version.


You can get the service manuals from Best Electronics:






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