PCCC function: logical read with three address fields

Hi!

I'm trying to understand the structure of the "Protected Typed Logical Read with Three Address Fields" function, and I am using the online DF-1 and PCCC documentation.

According to DF-1 Protocol and Command Set I can understand the basic structure.

At the file type description I see the following:

Use one of the these values for this field. Do not use any other values; doing so may result in unpredictable results.
•80 83 hex: reserved
•84 hex: status
•85 hex: bit
•86 hex: timer
•87 hex: counter
•88 hex: control
•89 hex: integer
•8A hex: floating point
•8B hex: output logical by slot
•8C hex: input logical by slot
•8D hex: string
•8E hex: ASCII
•8F hex: BCD

Click to expand...

When I connect RsLogix 500 to my PLC, I see this kind of packets with file types that are not in the list.
For example:
The following data of the pccc packet:
07 4d 00 44 4c b9 2c 0f 00 5c 1a a2 2c 00 00 00 00

The structure should be:
Byte Size = 0x2c
File Number = 0x00 (Output Image)
File Type = 0x00
Element Number = 0x00
Subelement Number = 0x00

Is it correct? How can the file type be 0?

Another example:
07 4d 00 44 4c b9 2c 0f 00 aa 1a a2 40 03 45 00 50
Here the file type is 0x45, again - undocumented

The published documentation generally only gives you enough information to read/write data table values. What you are seeing are system files that are not publicly documented. Some of these are things like the data table directory.