Certain registers must be read as a "block" from the PM1000, PM1200, and EM6400 meters. In order to read these registers, one must set the starting register to 3001, then 20 registers must be read in a single read. Attempting to read these registers in any other manner will result in either a time out or an error.The example in the picture below shows an scenario.

Note: "Function Code: O3H Read" is stating that these registers are Holding Registers.
The PowerLogic PM1000 Series Power Meters User Manual can be found here. It includes the PM1000/PM1200/EM6400 register list.