On 06/06/2018 09:31 AM, Noel Chiappa via cctalk wrote: Ah, Noel, you beat me to it--I wasn't even through my morning coffee before I read the query. Yes, a simple 5x7 scheme in an 8x8 "grid", which produced very readable output in small characters, but as you went to medium or large characters, the coarseness was immediately obvious. Still, pretty remarkable for 1964, a 64-character line with 64 lines of small characters possible. The 6602 programming reference is here: http://bitsavers.informatik.uni-stuttgart.de/pdf/cdc/cyber/peripheralCtlr/6… The gotcha, of course, is that you were driving the display with a 12 bit PPU with 4K words and a 1 microsecond cycle time. No buffering--you looped in your display code to refresh the display. This was no storage device--if you didn't make the loop or your code hung, the display blanked completely at worst, or flickered severely at best. Although the "dot" resolution for graphics was 512x512, drawing of involved graphics took a long time, so, even on simple games, such as BAT (baseball), was a mixture of characters and pixel graphics. The display for CHESS 3.0 was mostly made up of characters-as-graphics. For example, to shade a square on the chessboard, the "/' character was used. This need for continual refresh made for complex displays having some degree of flicker. The same PPU that generated both screen displays (and there were quite a number of them for the operator--the default was the AB display setup, scrolling master dayfile on one side and control point status on the other) also had to handle operator commands entered of the PPU program) had to poll the keyboard as well. As if that weren't enough, DSD also performed auto-completion of operator commands. Overlays were either loaded from disk (by calling another PPU to do the I/O) or directly from central memory. Space in the DSD driver was very tight, to the extent, I believe, that much of the memory taken by the PP resident was reclaimed by DSD. After all, DSD was loaded at deadstart and never unloaded. Like PP0, the system monitor MTR, it was there for the duration. There was also a user-callable PP program, called "DIS" that interpreted data from a user's CM area. DIS was granted access to the 6602 only with DSD temporarily giving it up. DIS was loaded only as needed. --Chuck P.S. Somewhere, I ran across a 1967 (granted) patent that describes the character generator scheme.