3300 ACM Installation and Operation Manual Power Measurement Ltd.
Appendix G: Serial Communications Protocol G-3
For example, if the 3300 ACM is responding to a read
command for which the requested register is the current input
scale of the meter at address 0A03 hex, the first command in
the data field from the 3300 ACM will be to select page 10 (0A
hex):
0A,00,00,00
Change to Command written
new page 10 to register 0
Once page 10 has been indicated, the requested data on that
page will be sent:
88,13,00,03
Requested data is Low order data
001388 hex register address 03
The data received by the Master Station is a current scale
value of 001388 hex (5000Amps decimal).
2.2.5 MESSAGE TERMINATION FIELD
The Message Termination Field is fixed in length and contains
only 1 byte. This byte is an eight bit error code used to detect
packets that have been corrupted during transmission.
The error code is an eight bit Longitudinal Redundancy Check
(LRC) which is complemented prior to transmission.
The LRC is calculated by a simple arithmetic sum over all
preceding message bytes contained within the packet with the
exception of the eight bit sync sub-field. The sum is then
complemented to yield the LRC byte.
The data register contains only the least significant (low
order) register address byte. A special command is used to
access registers on different pages. In this way, the entire
data field will be composed of specific register values inter-
spersed with page change commands.
REGISTER PAGING: REGISTER WRITE COMMANDS
The write command will always begin writing on page 0
(zero). Register writes from the Master Station to the 3300
ACM registers contain the low order register address byte in
Byte 4 of the register.
In order to change pages, the new page number must be
written into Byte 1 of register 0 of the current page. The only
registers which can be written to are on page 10 (meter setup
parameters), so the first data write command must always be
a page change to page 10.
For example, to change the current input scale of a meter the
address 0A03 hex must be written to. To select page 10 (0A
hex), the first data command must be:
0A,00,00,00
Change to Command written
new page 10 to register 0
Once page 10 has been selected to change the current scale to
a value of 001388 hex (or 5000Amps decimal), the second
data command must be:
88,13,00,03
Write new data Write to low order
001388 hex register address 03
REGISTER PAGING: REGISTER READ COMMANDS
The 3300 ACM response to a read command will always
begin on page 0 (zero). If the first valid requested register is
not on page 0, a page change will occur immediately. Similar to
the page change command described above, the new page
number is written into Byte 1 of register 0 of the current page.
The response data fields will contain the low order register
address byte in Byte 4 of the register. All valid registers on
that page will be sent, then the 3300 ACM will change to the
next page by sending a page change command.
This will repeat until all requested data has been sent, or the
packet is full.
Courtesy of NationalSwitchgear.com
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