[atari7800] Re: [personal] First post and a question

  • From: "Dan Boris" <dboris@xxxxxxxxxxx>
  • To: <atari7800@xxxxxxxxxxxxx>
  • Date: Thu, 13 Mar 2008 17:03:48 -0400

I think the 6/9 already includes the 3 cycle character map access. A single
graphics byte takes 3 cycles, an indirect 1 byte (1 character map, 1
graphics data) takes 6 cycles, and an indirect 2 byte (1 character map, 2
graphics data) takes 9 cycles. 


-----Original Message-----
From: atari7800-bounce@xxxxxxxxxxxxx [mailto:atari7800-bounce@xxxxxxxxxxxxx]
On Behalf Of bob.montgomery@xxxxxxxxxxx
Sent: Thursday, March 13, 2008 3:14 PM
To: atari7800@xxxxxxxxxxxxx
Subject: [personal] [atari7800] First post and a question


I posted a question on AtariAge here:

But I thought I would ask it here also.

The MARIA doc is a little confusing on DMA cycle timing:
All times listed below refer to 7.16 MHz cyles.

          DMA startup            5-9      cycles

          Header (4 byte)        8        cycles
          Header (5 byte)        12       cycles

          Graphics Reads:
          Direct                 3        cycles
          Indirect/1 byte        6        cycles
          Indirect/2 byte        9        cycles

          Character Map access   3        cycles

          Shutdown Times:
          Last line of zone      10-13    cycles
          Other lines of zone    4 - 7    cycles

Specifically, the "Character Map access 3 cycles" line.  Is that in addition
to the 6/9 cycles for an indirect graphics read or is it already included in
the 6/9 cycles listed there?


-Bob Montgomery

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  • » [atari7800] Re: [personal] First post and a question