Rockwell Automation 1775-S5_SR5,D17756.5.5 User Manual PLC-3 FAMILY I/0 - Manual (Page 142)

Binary Command Language
Appendix A
A-14
Most BCL commands and responses that require an address as one of the
parameters use the extended address format. The exceptions are:
read I/O word command which requires an I/O address
read block physical and write block physical commands (used for
uploading and downloading respectively) which use physical addresses
A detailed description of processor extended addressing appears in the
PLC-3 Family Controller Programming Manual (publication 1775-6.4.1).
Processor memory organization is summarized in Table A.E.
When you send an extended address to the processor, it must follow a
mask byte. The mask byte tells the processor which address levels the
following address defines and which levels default.
A bit in the mask which is set to: Indicates that the:
1 corresponding level of memory is specified in the
address to follow
0 default value is used for the corresponding level
of memory
Bit 0 in the mask corresponds to the major area. Bits 1 to 7 in the mask
each correspond to the next level in the specified section.
For example, in the data table (area 3), bit 1 corresponds to the context and
bit 2 corresponds to the data table section (e.g., output, input).
You can extend the mask byte into a mask word to specify more than 7
levels of an address by sending a byte with the value FF hex followed by
two bytes of the mask word. This is for future expansion of processor
extended addressing, as only 6 levels are presently used (Table A.E).
The default value for: Is :
the major memory area (bit 0) 3 (data table)
context (bit 1) initially the context that the processor is operating
when communication is established
all other memory levels 0
You can change the default context by using the set operating context
command. Unless otherwise specified, examples in this chapter assume
that the default context is 1. You can use the default for any level except
the lowest level of the address.
Extended Addressing