Toshiba VF-A7 10.8 Performance Tips

10.8 Performance Tips

This section offers several configuration tips which can help to optimize the performance of communications with the ETH-100 and attached drives.

1.Configure Modbus programmable pointer registers to also be drive scan registers. In the example configuration shown in Table 3, Modbus registers FC00 ~ FC07 are configured to point to the ASD scan registers. In this case, a Modbus transaction beginning at address FC00 with a length of 8 can be processed extremely fast. Of course, pointer registers can still be accessed if they are not configured as scan registers, but the transactions are slower, as they require transferring the request to the drive for processing.

Table 3: Efficient Scan/PPR Configuration

ASD Scan Registers		Modbus Pointer Registers
Register	R/W Value	Register	Points To…
FA01	Read	FC00	FA02
FA00	Read	FC01	FA01
FD00	Read	FC02	FD01
FE01	Read	FC03	FE02
FC90	Read	FC04	FC91
FE03	Read	FC05	FE04
FE42	Read	FC06	FE43
FA22	Read	FC07	FA23

2.Don’t leave a gap in the access sequence. For optimal network response, make sure all of the pointer registers that you are going to access are also configured to be ASD scan registers. The ETH-100 is most effective when all of the pointer registers that are going to be accessed are also ASD scan registers. In the example shown in Table 4, the high-speed processing of a Modbus register read starting at register 0xFC00 with a length of 8 will be delayed by the necessity to interact with the drive to obtain the values of drive registers 0xFC90 and 0xFE03.

Table 4: Inefficient Scan/PPR Configuration

ASD Scan Registers			Modbus Pointer Registers
Register	R/W Value		Register	Points To…
FA01	Read		FC00	FA02
FA00	Read		FC01	FA01
FD00	Read		FC02	FD01
FE01	Read		FC03	FE02
			FC04	FC91
			FC05	FE04
FE42	Read		FC06	FE43
FA22	Read		FC07	FA23
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