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ACH550-UH User’s Manual
Serial Communication – EFB
Mailbox Read/Write
The ACH550 provides a “Mailbox” function to access parameters that have not been
pre-defined by the protocol. Using mailbox, any drive parameter can be identified
and read. Mailbox can also be used to adjust parameter settings by writing a value to
any parameter identified. The following table describes the use of this function.
1. As noted above, Modbus provides direct access to all parameters using the format: 4 followed by
the parameter number.
2. BACnet not defined at time of publication.
Actual Value Scaling
The scaling of actual values can be protocol dependent. In general, for Actual
Values, scale the feedback integer using the parameter’s resolution. (See
"Parameter Descriptions" section for parameter resolutions.) For example:
Where parameters are in percent, the "Parameter Descriptions" section specifies
what parameter corresponds to 100%. In such cases, to convert from percent to
engineering units, multiply by the value of the parameter that defines 100% and
divide by 100%. For example:
1. Assuming, for the sake of this example, that the Actual Value uses parameter 9908
MOT
NOM
SPEED
as the 100% reference, and that 9908 = 1500 rpm.
2. Assuming, for the sake of this example, that the Actual Value uses parameter 9907
MOT
NOM
FREQ
as the 100% reference, and that 9907 = 500 Hz.
Although Actual Value scaling could differ from the above for the N2, FLN and
BACnet protocols, it currently does not. To confirm, see the following sections, as
appropriate:
Name
Description
Protocol Reference
Modbus
1
N2
FLN
BACnet
1
Mailbox
Parameter
Enter the number of the drive parameter
to access.
Does not
apply.
AO19
95
Mailbox
Data
Contains the parameter value after a
read, or enter the desired parameter
value for a write.
AO20
96
Mailbox
Read
A binary value triggers a read – the value
of the “Mailbox Parameter” appears in
“Mailbox data”.
BO19
97
Mailbox
Write
A binary value triggers a write – the drive
value for the “Mailbox Parameter”
changes to the value in “Mailbox data”.
BO20
98
Feedback
Integer
Parameter
Resolution
(Feedback Integer) * (Parameter Resolution) = Scaled Value
1
0.1 mA
1 * 0.1 mA = 0.1 mA
10
0.1%
10 * 0.1% = 1%
Feedback
Integer
Parameter
Resolution
Value of the
Parameter that
defines 100%
(Feedback Integer) * (Parameter Resolution) *
(Value of 100% Ref.) / 100% = Scaled Value
10
0.1%
1500 rpm
1
10 * 0.1% * 1500 RPM / 100% = 15 rpm
100
0.1%
500 Hz
2
100 * 0.1% * 500 Hz / 100% = 50 Hz
