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38 203987 Rev A RCP2-1000 RM Remote Controller Operations Manual
5.1.3.1 Frame Check
The Frame Check field provides a checksum during packet transmission. This value is
computed as a function of the content of the destination address, source address and
all Command Data Substructure bytes.
In general, the sender formats a message frame, calculates the check sequence, ap-
pends it to the frame, then transmits the packet. Upon receipt, the destination node re-
calculates the check sequence and compares it to the check sequence embedded in
the frame. If the check sequences are the same, the data was transmitted without er-
ror. Otherwise an error has occurred and some form of recovery should take place. In
this case, the amplifier will return a packet with the “Bad Checksum” error code set.
Checksums are generated by summing the value of each byte in the packet while ig-
noring any carry bits.
A simple algorithm is given as:
Chksum=0
FOR byte_index=0 TO byte_index=packet_len-1
Chksum=(chksum+BYTE[byte_index]) MOD 256
NEXT byte_index
5.1.4 Timing issues
There is no maximum specification on the inter-character spacing in messages. Bytes
in messages to amplifier units may be spaced as far apart as you wish. The amplifier
will respond as soon as it has collected enough bytes to determine the message. Gen-
erally, there will be no spacing between characters in replies generated by unites. The
maximum length of the packet sent to the amplifier node should not exceed 64 bytes,
including checksum and frame sync bytes. Inter-message spacing must be provided
for good data transmission. The minimum spacing should be as long as the time re-
quired for transmitting five (5) bytes at the current baud rate. This time is required for
the controller to detect a “Line Cleared” condition with half duplex communications.
For more information, see the Paradise Datacom Solid State Power Amplifier 4RU
Chassis Operations Manual, document number 201627.
HEADER TRAILER
DATA
(4 Bytes) (6 - 32 Bytes)
(1 Byte)
1 Bytes
FRAME CHECK
Checksum
Figure 5-4: Trailer Sub-Packet