Toshiba G7 - Manual (Page 44)

G7 ASD Multi-Protocol Communication Option and PG Feedback Option Manual 37
10.2 Modbus RTU
10.2.1 Configuration
Besides the Modbus network selection and configuration parameters (F890-F894) described in Section
8.2, the only other ASD parameter requiring configuration is the ASD’s “Inverter Number” parameter
(F802). This parameter setting is used as the drive’s Modbus station address.
Some important points to note regarding parameter F802:
• Parameter F802 is only validated after a drive reset. Therefore, if this parameter is changed,
remember to reset the drive to validate the change.
• The standard factory setting for parameter F802 is 0, which is reserved for Modbus broadcast
transmissions. To be valid, this parameter must be set to a value between 1 and 247. If parameter
F802 is 0 or 248
∼ 255 when Modbus communications are initialized, the Multicom interface’s
“Network Status” LED (the lower LED) will flash red to indicate the configuration error, and
network communications will not be enabled.
If ASD control (frequency command input, RUN/STOP, etc.) is to be performed via the Modbus
network, then the drive’s Command Mode Selection and/or Frequency Mode Selection parameters must
be configured to use the communication card as the drive’s command source location, or the “option
priority” bits of the basic command word (Modbus register 0x0A07) must be set accordingly. For
information on the specific setting methods and values of the Command Mode and Frequency Mode
Selection parameters, please refer to the G7 Adjustable Speed Drive Operation Manual.
10.2.2 Communication Formats
A brief note about Modbus communication formats: According to the Modicon Modbus Protocol
Reference Guide, the specifications for the Modbus RTU communication mode is as follows:
Coding System: ............... 8-bit binary, hexadecimal 0
∼ 9, A ∼ F
Two hexadecimal characters contained in each 8-bit field of the message
Bits per Byte: .................. 1 start bit
8 data bits, least significant bit sent first
1 bit for even/odd parity; no bit for no parity
1 stop bit if parity is used; 2 bits if no parity
Error Check Field: ......... Cyclical Redundancy Check (CRC)
According to the Modicon Modbus specification, therefore, the number of bits per byte in RTU mode is
1 start + 8 data + 1 parity + 1 stop (if parity is used), or 1 start + 8 data + 2 stop (if parity is not used),
resulting in an RTU data frame that is fixed at 11 bits per byte.
In addition to these standard specified data frame sizes, the Multicom Modbus interface offers an
optional configuration of providing for only 1 stop bit when no parity is selected. As indicated in Table
6 on page 17, by setting parameter F892 (Parity & Stop Bits) to “0”, the RTU data frame size is
modified to consist of 1 start + 8 data + 1 stop bit = 10 bits per byte.