Implements Read Multiple Holding Registers, Read Multiple Input Registers, and Write Single Holding Register.
This uses and comes with Duane Degn's 512 byte buffer version of Tim Moore's original 4 port serial driver. Anything descended from Tim Moore's driver should work fine, but I've only tested it with Duane Degn's version. Duane Degn also has a 128 byte rx buffer per port version, if you need the ram for other things.
I somehow ended up with two versions of this driver. I merged them and posted the result here. The two versions that went into the merge both worked, but I haven't tested the result, so please PM me (Electrodude) on the Parallax Forums if you have any problems.