Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 226)

13–11 PLC Addressing
Publication 1770Ć6.5.16 - October 1996
PLC-5 Logical Binary Addressing
Byte Contents
1 the mask byte
This byte determines which four levels of the address are specified.
The mask is read from the LSB to the MSB. If a level of an address is not
specified, it uses the default value, which is always 0, except for the file
number which has a default of 1.
You must always specify the last level of an address (even if it is a 0) so that
the actual number of levels in a particular address can be determined.
A 1 in the mask bit corresponding to a particular address level signifies that
that particular address level is encoded in the bytes which follow. Only those
address levels with a 1 in the corresponding mask bit are encoded.
For example:
• 00001111 means that there are 4 levels in the address and all 4 levels are
encoded
• 00000101 means there are 3 levels in the address and level 2 uses the
default value (the default is always 0 for level 2). Only levels 1 and 3 are
encoded.
This byte is required.
2 the first level of the address not using the default value
...N up to 4 levels of addressing
Important: If the value of the mask or a level of the address is
greater than or equal to 255, you cannot encode it into 1
byte. You must flag this case by programming an FF
hex at the level address to signify that the level address
is greater than or equal to 255 and the next 2 bytes will
contain the level address. Then, code the level into the
following two bytes. After 255 (FF hex), you send the
bytes with low byte first, high byte second.
The following figures show examples of PLC-5 logical binary
addresses.