CityGrow CG102RS232, Руководство пользователя

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When the sender is desired to receive an acknowledgment from the receiver to confirm the
data is received correctly, the sender shall set the AckReq of the frame control field to ‘1’.
Otherwise, the AckReq should be ‘0’.
When the receiver received a complete data frame correctly with AckReq is set to ‘1’, the
receiver shall reply the sender with an acknowledgment frame with the IsAck set to ‘1’
immediately. The format of the acknowledgment frame is shown in Figure 3-4.
Sync Length
Frame
Control Seq.
No.
2 bytes 1 byte 1 byte 1 byte
Check Sum
2 bytes
0x19 0xC3 0x03 0 1 0
1 byte
Paddin
g
0x00
Figure 5-4 Frame format of the acknowledgment frame
Besides the acknowledgment frame, the IsAck shall always set to ‘0’ in the “Frame Control”
of any data frame.
5.4. Seq. No.
The 1-byte sequence number is used to identify different data frame during communication.
The sequence number is generated by the sender and the value is started from 0. The value
of the sequence number is increment by one for each new data frame and it should be
reset to 0 after the value is larger than 255. When the data frame is required to be
acknowledged, the receiver should fill the “Seq. No.” of the acknowledgment frame with
the received “Seq. No.” from sender. The example shown in Figure 3-6 elaborates the
general operation of the sequence number with the acknowledgement.
5.5. Padding
The 1-byte padding is reserved. In current version, the value of padding field should always
be ‘0’.
5.6. Payload
The variable length payload is used to place the Protocol Data Unit of ZDCP.
5.7. Check Sum
The 2-byte check sum code is used to identify the correctness of the received data frame.
The computation of the check sum is the summation of the entire byte which is counted
from “Length” to the end of “Payload”. The 2-byte summation result is placed into the field
with Lower byte first and Upper byte end. For example, if the result is 0x1234, the check
sum should be:
0x34 0x12
1 byte 1 byte
Check Sum
Figure 5-5 The contain of check sum field if the summation result is 0x1234