15
Address domain is located at beginning of frame, composed of one byte (8 bit binary system domain),
Decimal system is 0~255, in
the ACR meters, just 1~247 is used, other address is Reserved, these bits indicate terminal
device address specified by users , this device
will receive the connecting host computer data. Every terminal device has its only one address, only the addressing terminal is
responding enquiry including this address. When terminal is transmitting one responding, the responding slave address data tell host
computer that which terminal is communicating with it.
6.2.3 Function (Function) domain
Function domain: function domain tell the addressed terminal to execute what function. Below table list: function domain used in
this Series meters, and their meaning and function.
Code(hex)
Meaning
Operation
03H
Read holding register
Obtain current binary system value of one or multiple holding register
10H
Present multiple register Set actual binary system value into a series of continuous holding register
6.2.4 Data (Data) fields
Data field
：
data field is including the data needed by terminal for executing specific function, or the collected data when terminal is
responding enquiry . Content of these data may be value, reference address or setting value.
For example: The function domain tell terminal to Read one register, the data field need to specify the starting register and Read how
many data, the built-in address and data have different content depending on type and slave computer.
6.2.5 Error check (Check) domain
This domain adopt CRC16 cyclic redundancy check, for host computer and terminal, the error in checking and transmitting is
allowable. Due to electric noise and other interfere, when one group of data is transmitting from one device to another device, on the
transmitting line, some change may be produced. The error check can enable the host computer or slave computer not responding those
changed data, so, safety, reliability and efficiency of system are upgraded.
6.3 Method
to create error check code (CRC)
Error check (CRC) domain occupy 2 byte, including one 16 bit binary system value. CRC value is calculated by transmission
device, then attached to the data frame, the receiving device, while receiving, it calculates the CRC value again, then comparing it with
the receiving CRC domain value, if these two values is not equal, it shows a error occurs.
When operating, firstly, preset one 16-bit register
as
All-1, then continuously operating each byte 8 bit of Data frame and current
value of this register, only
every 8 data bit of each byte to participate in forming CRC the start bit and stop bit and usable parity bit
have
no affect on the CRC. When forming CRC
,
every 8 data bit of each byte and content of register carry out exclusive or operation, then
shift the result to the
low bit the high bit is filled with 0, shift out the least significant bit (LSB) is shifted out and tested, if it is 1
，
this
register and one preset fixed value (0A001H) carry out one exclusive or operation, if the least significant bit is 0
，
no treating is needed.
Flow for forming one CRC:
1
、
Preset one 16 bit register as OFFFFH (All-1), called as CRC register.
2
、
8 bit of data frame first byte and low byte of CRC register carry out exclusive or operation, then save its result back to CRC
register.
3
、
Right shift CRC register for one bit, the most significant bit is filled with O
1
the least significant bit is shifted out and tested.
4
、
If the least significant bit is 0, Repeat the third step (next shift); If the least significant bit is 1, CRC register and preset fixed value
specified (0A001H) carry out exclusive or operation.
