Toshiba VF-A7 - Manual (Page 33)

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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