DEC have given us a new tube with a P4 phosphor, as the old one did not focus well at the edges of the screen, and a new set of push buttons which work well. The BSI is still giving the occasional illegal interrupt and there are some minor bugs in DOS V2A.
The BSI gives illegal interrupts on the PDP 15 while the 1906A interface (7203) is turned off and the link cables are plugged in. The cables are not terminated properly when the 7203 is off, and can then pick up any stray inductance pulses.
The 7203 must therefore be switched on whenever the PDP5 is in use.
There are still illegal interrupts with the 7203, though these come at the rate of 3 or 4 a day while the Fixed Disk of the 1906A is on. The motor of the FDS is 10BHP ,so switching it on or off generates a mains spike. While the FDS was off for maintenance, and the 7203 on, there were no illegal interrupts on the PDP15.
1. If you use the L or N switch in Macro to list programs on the Display, the computer freezes after Pass 1. It can only be re-awoken by typing CTRL C.
Tabs are incorrect on listing files on the Display. A typical macro line is:
MYLABzt <tab> LAC<tab> FRED<tab>/COMMENT
On the teletype this appears as
col 1 8 16 24 MYLABL LAC FRED /COMMENT
On the Display as
1 8 16 24 32 MYLABL LAC FRED /COMMENT
The new VDU and operating system cause some problems and solve two. The problem which is solved concerns the light pen and focussing. The light pen will now hit through the smoked glass screen which covers the tube of the VTO4. Previously this had worked for some programs and not others. Focussing at the edges of the screen is now good. The main problem which this new phosphor has created is flicker. If the sync bit is on a certain amount of information can be displayed with out too much flicker. This is the amount that can be displayed in the time between sync pulses. The display time is dependent upon the total length of vectors drawn and the number of Setpoints performed. Once the time to display the display file exceeds the sync time the flicker becomes very bad because the display file is not restarted until the next sync pulse. In some cases the screen goes completely blank when even more vectors are drawn.
FRAH's Font defining program works very well, and seems to show more data flicker free than before. It never uses more than a dozen SETPT's per frame.
The repeatability of the new tube is good but the characters no better than before. Peter Danahay says that he should be to improve the characters.
Flicker disappears when vertical vectors are drawn, and only happens with horizontal or diagonal vectors.
JRG's VIE program is badly affected at low intensities. He intends to increase the intensity to improve the situation. Otherwise, if a long film is used the viewer will almost certainly go away with a headache.
