1.1 --- a/ULA.txt Tue Apr 11 15:46:32 2017 +0200
1.2 +++ b/ULA.txt Wed Apr 12 16:09:28 2017 +0200
1.3 @@ -1067,8 +1067,8 @@
1.4 208 26 x3 26 26 256 &62C0 -> &6200
1.5 208 26 x3 26 13 16 &6460 -> &6400
1.6
1.7 -Enhancement: Text-Only Modes using Cached Character and Attribute Data
1.8 -----------------------------------------------------------------------
1.9 +Enhancement: Text-Only Modes using Character and Attribute Data
1.10 +---------------------------------------------------------------
1.11
1.12 In modes 3 and 6, the blank display lines could be used to retrieve character
1.13 and attribute data instead of trying to insert it between bitmap data accesses,
1.14 @@ -1084,6 +1084,24 @@
1.15 However, the CPU would not benefit from having any extra access slots due to
1.16 the limitations of the RAM access mechanism.
1.17
1.18 +A scheme without caching might be possible. The same line of memory addresses
1.19 +might be visited over and over again for eight display lines, with an index
1.20 +into the bitmap data being incremented from zero to seven. The access patterns
1.21 +would look like this:
1.22 +
1.23 + Reads: C B C B C B C B C B C B C B C B ... (generate data from index 0)
1.24 + Reads: C B C B C B C B C B C B C B C B ... (generate data from index 1)
1.25 + Reads: C B C B C B C B C B C B C B C B ... (generate data from index 2)
1.26 + Reads: C B C B C B C B C B C B C B C B ... (generate data from index 3)
1.27 + Reads: C B C B C B C B C B C B C B C B ... (generate data from index 4)
1.28 + Reads: C B C B C B C B C B C B C B C B ... (generate data from index 5)
1.29 + Reads: C B C B C B C B C B C B C B C B ... (generate data from index 6)
1.30 + Reads: C B C B C B C B C B C B C B C B ... (generate data from index 7)
1.31 +
1.32 +The bandwidth requirements would be the sum of the accesses to read the
1.33 +character values (repeatedly) and those to read the bitmap data to reproduce
1.34 +the characters on screen.
1.35 +
1.36 Enhancement: MODE 7 Emulation using Character Attributes
1.37 --------------------------------------------------------
1.38
1.39 @@ -1101,7 +1119,8 @@
1.40 at least make a limited 40-column multicolour mode available as a substitute
1.41 for MODE 7.
1.42
1.43 -Using the text-only enhancement with caching of data, the storage requirements
1.44 +Using the text-only enhancement with caching of data or with repeated reads of
1.45 +the same character data line for eight display lines, the storage requirements
1.46 would be diminished substantially:
1.47
1.48 Screen width Columns Rows Bytes (C) Bytes (A) Colours Screen start