Two SX's sharing the same SRAM?

Comments

• Peter Verkaik Posts: 3,956

  2006-09-07 14:05 edited 2006-09-07 14:05

  There are special ic's to do just that:
  http://www.maxim-ic.com/appnotes.cfm/appnote_number/62
  
  Other options is to multiplex signals yourself. The above article
  also talks about that.
  
  regards peter
• cbmeeks Posts: 634

  2006-09-07 14:20 edited 2006-09-07 14:20

  Thanks!
  
  cbmeeks
  
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• Bean Posts: 8,129

  2006-09-07 14:44 edited 2006-09-07 14:44

  cbmeeks,
  · Dual ported memory is nice, but it's expensive.
  · Is this for video ?
  · One SX48 is the video generator and the other updates the screen ?
  
  What I was thinking of doing is this:
  
  Game SX gets it's clock from the Video generator SX output pin. (Timer output?)
  Video generator SX has the address lines connected directly.
  Game SX has the addres lines connected through resistors (4.7K ?).
  
  The video generator makes it's address line INPUTS when not accessing the memory.
  
  When the video generator needs to access the memory is does the following:
  · Stops the game SX clocks
  · Makes it's address lines outputs and puts the address on the pins (overriding the game SX).
  · Reads the memory for 1 line of video into the SX RAM.
  · Makes it's address lines inputs again.
  · Starts the game SX clock again.
  
  The SRAM control signal would work the same way, through resistors on the Game SX.
  
  It was a plan, I haven't attempted to make it work.
  
  Bean.
  
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• cbmeeks Posts: 634

  2006-09-07 15:00 edited 2006-09-07 15:00

  Well, for video and more (audio, IO, etc).
  
  my plan was to have an SX48 as a video processor. His only job is to render what is in a video buffer...one pixel at a time.
  
  Then have another SX48 for writing data to that buffer during the verticle blank.
  
  My CPU is going to be a 6502
  
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• Dave Hein Posts: 6,347

  2006-09-07 15:32 edited 2006-09-07 15:32

  Use one pin from the video SX to tell the other SX when its OK to write in the memory. This could include the horizontal blanking period as well. The enable signal would need to be shut off a few cycles before the end of blanking to ensure that the writing SX has released the busses.
  
  Dave
• cbmeeks Posts: 634

  2006-09-07 15:35 edited 2006-09-07 15:35

  That's what I was thinking. maybe make one pin an input and the other an output? That way, if the input is receiving voltage, then shut down and wait. That would put the control in one SX...which is what I want.
  
  For example, the SX rendering the video signal could control when the other SX is allowed to write...it could set the output pin to high while it's in the vertical blank
  
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