Watlow Silver Series Addendum - Manual (Page 6)

Silver Series OIT  6  Watlow Addendum
Parameter Register Addresses
The Modbus RTU and Modbus TCP communications protocols assume that each device’s memory is
organized in blocks of like-data. Each data block contains either read-only data or read/write data and
either bit-size data or word-size (16-bit) data. For example, the Coils data block contains read/write bits
and the Input Register data block contains read-only words.
Within each of these data blocks there is a range of memory locations. The data blocks are often referred
to by the first digit of their address range. For example, the Holding Registers are often referred to as,
“the 4x registers”. The Modbus standard defines both a numbering scheme and an addressing scheme for
the memory locations in the data blocks. The table below illustrates this information for the four most
commonly discussed data blocks.
Name Number Access
Data
Size
Memory Location
Numbers
(Absolute)
Memory Location
Addresses
(Relative)
Coils 0x Read/Write 1 bit 1 to 65,536 0 to 65,535
Discrete Inputs 1x Read-Only 1 bit 100,001 to 165,536 0 to 65,535
Input Registers 3x Read-Only Word 300,001 to 365,536 0 to 65,535
Holding Registers 4x Read/Write Word 400,001 to 465,536 0 to 65,535
Because the location numbering scheme includes the data block number, it is helpful to think of it as an
absolute address. The absolute address specifies the address completely or absolutely in that it says
which data block and which address contains a piece of data. Because the location addresses do not
include the data block number, it is helpful to think of them as relative addresses. They specify where to
look relative to the starting point of the data block.
Some software and device manufacturers document the use of their products in terms of the numbering
scheme while others use the addresses. In either case the manufacturer typically calls the numbers he
supplies, “the addresses.” So to use any two products together you need to know whether or not you
have to convert the specified “address” in order to get the result you want.
EasyBuilder5000’s Modbus drivers call the data block, “Device type” and for “Address” expect the
memory location’s absolute address without the data block number. For example, to access a value in a
holding register with absolute address 401,905, for Device type you select the data block “4x” and enter
“1905” in the Address field. The following illustrates setting this address in EasyBuilder5000.
(072)
Watlow controllers use only the 4x registers. Therefore, you will set the Device type to 4x to access any
parameter in a Watlow controller. Watlow manuals specify relative addresses. Therefore, you must add
one (1) to an address found in a Watlow manual (other than this manual) before you enter it in
EasyBuilder5000.