This technical note describes the Modbus register mapping for the PLC IO Interface for GE Genius IO.

Modbus TCP/IP

The legacy module will be accessible via a TCP/IP connection using the Modicon Modbus protocol (Open Modbus TCP/IP specification). The access for each IO table will be by IO register address (words 300001-301500 (AI), 400001-401500 (AO) for analog tables (3-4), bits 1-25600 (DO) and 100001-125600 (DI) for discrete tables (1-2)).

Global status will be accessible in AO registers 401501 to 401900, and the configuration table will be accessible in registers 401901 to 402000.

GE Genus Table Set Definition

There are three types of tables. The first type of table is the “Global” legacy status group, while the second is the “IO Table” group containing only data pertinent to a specific IO type, and the third is the “configuration” table. The purposes and organization of these groups is described in this section.

The following sections give the detail organization for the layouts of the individual tables.

Open Modbus TCP/IP Dataset assignments

The data tables will be assigned modbus register (and coil) address for access using Modbus TCP/IP. These will be sequentially assigned to the IO Table registers. (note offsets are specified for the IO address in modbus messages, therefore DI 100001 is addressed as offset 0 in messages.

Global status registers (Table 0, sets 1-4) will be accessible in the AO table in registers 401501 to 401900. The configuration table (5) will be accessible through the AO table (401901-402000).

For Modbus TCP/IP communications the address is specified as an offset in the table (1 to 1500 for IO, 1501 to 1900 for global status, and 1901 to 2000 for configuration dataset).

Global (status) Set(s)

Ports 3 and 4 (Ethernet configuration port and Modbus TCP/IP port) have all 32 Blocks configured.

Global Table Set 1 Layout

This table set contains the global configurations and status data as well as the first nine (9) Block configuration and status words. See DS2 = Blocks 9-18, DS3 = Blocks 19-28, and DS4 = Blocks 29-32

Driver Status Words

This group is designed to display the current status of the GE Genus Legacy RIO driver.

Card Status Words

This group of register displays the current status of the S&S RIO card. Except for the Incremented CRC error value, these values are read only (cannot be changed).

Watchdog is enabled (bit 7 set (1)) if shared memory locations 0x0ABB is 0x47and 0x0ABC is ox45, otherwise watchdog is disabled (bit = 0)

Block Status Words

Each configured Block (see Block word in the command word section) contains 10 status words. These words display the current status of the Block.

Global Tables Sets 2 to 4 Layouts

The global status table sets 2 to 4 are required only if the status/configuration words for Blocks contained in them are required. The number of Blocks per port is specified in the configuration table (5), the current number is displayed in the global table set 1 word 5. Set 2 is required if more than 9 Blocks are configured for global table set group accessed, Set 3 for more than 19, and Set 4 if more than 29.

IO Data Table Sets (Tables 2-4)

There are four I/O tables. Each of the tables may contain from 1 to 15 sets, depending on the number that are required for capturing RIO module IO (data and status). This method allows up to 1500 words (or 3000 bytes) of data for each IO type (DI, DO, AI, and AO).

Each table set is addressed specifying its unique address:

Port Address:    3 for Ethernet port.

Each port accesses the global data words (words 1-10 of the global table set 1). The port also accesses the Block status words (11-100 of set 1 and 1-... of set 2 to 4) as specified in the global word 5. Each port can also access any portion of the IO table sets. Each IO table takes up the number of sets required to hold the number modules entered in the module configuration table (5) set 1.

Table Type:       Specify the type of table to access from the port. This is the DeltaV serial card “device”. The most significant 4 bits of the byte specify the Table ID (1-5), the least significant 4 bits specify the offset (1-15 (0x1 to 0xE).

* Total (sum of tables 1-5) is 28 to 32 depending on the number assigned to the global (0) group

Modules are assigned addresses in the IO data tables to hold their IO data. Inputs and Outputs are assigned separately. All address start on word boundaries. The controller specifies the address. This may be formatted with spaces between data to allow the global formatting of IO data so all modules will have IO data beginning at predefined addresses, or may be “packed” to optimize communications bandwidth. Modbus TCP/IP communications is rapid (10 to 100 MB).

IO Data bytes

All standard IO data from all GE Genius IO blocks is available at all times the bus controller is “on-line”. This data is captured by the µGENI IO card into shared memory (at C800). A portion of this memory is organized into two IO buffers, each holding blocks of 34 registers. One of these buffers holds all input data that each GE block sends each bus scan. The other buffer holds the output data that will be sent to the IO blocks (again each IO scan). The Legacy module does not simply map the IO buffers into the IO tables, instead it allows the controller to configure the starting location for each IO block data to be stored. The number of bytes actually assigned depends on the module definition associated with the block. This allows the maximum of flexibility in assigning addresses. See the discussion of configuration of the legacy module.

Circuit status bytes

Modules may also be assigned “Status” bytes to hold the status information returned for each circuit. These extra bytes data are assigned to the input data table. These hold the module status (or fault) information, based on the type of block. These bytes are assigned to the AI or DI table (depending on the table selected for IO data).

Each block will be associated with at least one byte of status data. This data contains the status of the legacy driver, the mode of the driver, and the block present bit status, as well as block status bits returned from the block (if communicating). This byte should be zero (0) if communications is occurring and block is functioning correctly. If a failure occurs the byte will be non-zero, with the bit(s) signifying the fault.

Fault status is supplied as a datagram from each block, triggered when a block faults, after a reset (if block is still faulted), or in response to a read diagnostics datagram from bus controller. The report fault message (and read diagnostics response) messages all have a 4 byte header which includes the block type (model number) in byte 0 and the software revision of the block in byte 1. Then next 2 bytes include the block diagnostic data (byte 2 is currently defined for the blocks, byte 3 is not used. Byte 2 (block diagnostics) is displayed in the block status group (word 5) in the global status table. The remaining bytes in the message hold fault data for each of the circuits in the block as described below in block data definition sections.