24 Apr
2006
24 Apr
'06
3:10 p.m.
This is a little strange!
A HP1350 will plot vectors from 0 to 1022.
Hve you tried that for both coordinates?
I've not played with mine much, but from the manual, it appears there's
10 bit wide memory in there. Each endpoint/character takes up 2 memory
locations (hence the 2048 endpoints, it uses 4K RAMs). For endpoints, the
2 locations are simply the X and Y coordinates. For a chracter, one of
them (I forget which) is set to all 1's, the other is the ASCII code (7
bits) + attributes.
My guess, therefore, is that it should take from 0 to 1023 in one direction.
A HP1351 will not. It will plot vectors from 0 to 1020.
I need to retest this up to 1021 to see exactly where the
limit is.
Very odd. I suppose I'd should look at the service manual on hpmuseum.net
and see if I can sport the circuit that engorces this.
The program I'm using for this testing draws a box around
the limits of the display, and then two diagonal lines from corner
to corner. The result is a large box with an X through it.
When the 1351 'fails' to plot the box, only the left hand Y axis
vector is drawn. No letters appear.
When a 1350 tries to draw off the edge of the screen one
of two things happen.
Either a vector is drawn that wraps around, or a letter or
symbol is drawn in place of the out of bounds vector.
MY guess (and it is a guess) is that it truncates the value to 10 bits.
If they're all ones for the appropriate coordinate, the other coordinate
gets turned into a character. Otherwise it just wraps round.
I am not sure if there's any limit on the number of characters that the
BCD-bianray converter will handle. It may do odd things if given more than
4 digits.
-tony