10.3 Modbus/Drive Register Mappings
The ETH-100’s Modbus TCP/IP interface acts as a relatively straightforward network gateway for the attached drives. By and large, Modbus TCP/IP holding registers (04 registers) are directly mapped to corresponding Toshiba drive registers (also referred to as “communication numbers” in Toshiba documentation) with a direct 1-to-1 correspondence. The relationship between Modbus TCP/IP holding registers and their Toshiba drive register counterparts is as follows:
Modbus TCP/IP holding register = Toshiba drive register + 1
This means that in order to access a specific Toshiba drive register, simply add 1 to it and access that Modbus TCP/IP holding register. The reason for this offset is due to the fact that Toshiba drive registers begin at number 0, while Modbus holding registers begin at number 1.
As an example of this relationship, let’s say that we would like to access parameter “Acceleration Time #1” on a Toshiba S9 drive connected to the ETH-100. According to the relevant Toshiba Serial Communications Manual, we see that “Acceleration Time #1” resides at drive register number 0x0009 (note hexadecimal notation). By adding 1 to this value, we obtain 0x000A (1010), which is the Modbus holding register that must be used to access this drive parameter.
In order to avoid any possible confusion regarding this register-mapping scheme, this manual will always explicitly use the terms “drive register” or “Modbus register” where the intention may not be clear. If the term “register” is used alone, then “Modbus register” will be the intended meaning by default.
With only 2 exceptions (discussed below), the ETH-100 does not in any way modify or otherwise alter valid register access requests originating from the Modbus TCP/IP client. By adhering to this design parameter, the availability and interpretation of any Modbus registers is entirely determined by the attached drive(s). In this way, the ETH-100 allows itself to become virtually “transparent” on the network, essentially allowing the Modbus TCP/IP client to carry on a dialog directly with the drives. This technique also allows a wide array of drive families and capacity classes to be implemented without compatibility concerns.
The two exceptions to the previous paragraph are as follows:
1.Register remapping option. The ETH-100 can be configured to alter a portion of the mapping relationship for register-limited clients. Refer to section 10.4 for a discussion pertaining to register remapping.
2.The status register (drive register 0xFE01) typically does not contain any information indicating whether the attached drive is faulted or not. For ease of client application programming, therefore, the ETH-100 will indicate a connected drive’s faulted status in bit #14 of this register (normally, this bit is ”reserved” by the drive). Refer to Table 2 for an example modified status register from an S9 drive. Because the specific format of the status register depends on the drive family and firmware implementation, please refer to your drive’s Serial Communications Manual for the exact structure of this bit- mapped register. NOTE: This added feature is only available if drive register 0xFE01 is configured to be one of the selectable scan registers (refer to section 10.5 for more information regarding scan registers).
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