See also the back side of the Laser 2001 box.

Of course VTech may have manufactured several different plotters with the same look, if those connect directly to the expansion bus. I never quite figured out if the 200/300, 350/500/700 and the 2001 have different kind of expansion buses and pinouts.
Here is a somewhat badly OCR:ed article from Creative Computing, February 1984 which mentions the PP-40 with a Centronics parallel interface:
http://www.atarimagazines.com/creative/ ... inters.php
An advertisement (*) for the Laser 3000 which also refers to the PP-40:
http://www.1000bit.it/ad/bro/vtech/VTech-Laser3000.pdf
(*) By the way, VTech introduced a number of errors in the comparison on page 12. For instance, the C64 has both Microsoft BASIC, 2 cursor keys and upper and lower case characters. It is also noted that the 3000 a.k.a. CAT later on were shipped with external power supplies, as the internal one was unreliable - the same one as mentioned in the comparison as a benefit that it is built in instead of separate. I wonder about the 4 channel sound, some sources refer to it as 3 channels + 2 noises. I bet it is an ASIC copy of the AY chip, as it handles envelopes. That one kind of has 4 channels in the meaning three square waves and the option to run noise on top of one channel.