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7I76 48
REFERENCE INFORMATION
SPECIAL RPCS
All remotes that work with SSLBP must implement three special RPCs, the
ProcessDataRPC, The UnitNumberRPC, and the DiscoveryRPC.
DiscoveryRPC = 0xBB
B
Returns one byte that specifies process input data size in bytes,
and one byte that specifies the process output data size in bytes. Following the size bytes
are two 16 bit pointers, the first is the PTOC and the second is the GTOC. Note that the
remote software mode must be set before issuing the discovery RPC.
UnitNumberRPC = 0xBC
B
Returns 32 bit unit number
ProcessDataRPC = 0xBD -- Normal process data transfer RPC followed by output data
bytes. Returns one byte of remote fault information followed by input data. Number of input
and output bytes are as specified in the DiscoveryRPC.
CRC
LBP on the 7I76 uses CRC checking of all commands and data to insure validity.
The CRC used is a 8 bit CRC using the same polynomial as the Dallas/Maxim one wire
devices (X^8+X^5++X^4+X^0). The CRC must be appended to all LBP commands and all
returned data will have a CRC byte appended. Commands with no returned data (writes
or RPCs with no reads) will still cause a CRC byte to be returned, this CRC byte will always
be 00H.
FRAMING
Since LBP is a binary protocol with no special sync characters, the packet framing
must be determined by other methods.
Framing is done by a combination of timing and pre-parsing the serial data. Timing
based framing is used to reset the parser at gaps in the serial data stream. This provides
fast resynchronization to allow robust operation in noisy environments. The actual timeout
used needs to be optimized for the operating mode. In setup mode where a non real-time
OS may be communicating with the remote device, the frame timing is set to its maximum
value (25.5 character times). This is equivalent to 2.1 mS at 115200 baud. This means
that host communications cannot have more than 2.1 mS delays between characters in
a command sequence when in setup mode.
In operate mode, command timeout is set by SSLBP to be 4 character times (16
uSec at 2.5M baud). The SSLBP firmware always sends commands in bursts without inter-
character gaps so will always meet this timing. The timing is set short so that the parser
on the remote device will always be reset and ready for the next command at the highest
repetition rates even if data has been corrupted by noise so that incomplete commands
have been received.
Содержание 7I76
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