17.5.2 Principle of operation
The SPA bus uses an asynchronous serial communications protocol (1 start bit, 7 data
bits + even parity, 1 stop bit) with data transfer rate up to 38400 bit/s. For more
information on recommended baud rate for each type of IED, refer to Technical
reference manual. Messages on the bus consist of ASCII characters.
Introduction of SPA protocol
The basic construction of the protocol assumes that the slave has no self-initiated need
to talk to the master but the master is aware of the data contained in the slaves and,
consequently, can request required data. In addition, the master can send data to the
slave. Requesting by the master can be performed either by sequenced polling (for
example, for event information) or only on demand.
The master requests slave information using request messages and sends information to
the slave in write messages. Furthermore, the master can send all slaves in common a
broadcast message containing time or other data. The inactive state of bus transmit and
receive lines is a logical "1".
SPA protocol
The tables below specify the SPA addresses for reading data from and writing data to
an IED with the SPA communication protocol implemented.
The SPA addresses for the mA input service values (MIM3 to MIM16) are found in
table
629.
Table 629: SPA addresses for the MIM function
Function block
SPA address
MIM3-CH1 4-O-6508
MIM3-CH2 4-O-6511
MIM3-CH3 4-O-6512
MIM3-CH4 4-O-6515
MIM3-CH5 4-O-6516
MIM3-CH6 4-O-6519
MIM4-CH1 4-O-6527
MIM4-CH2 4-O-6530
MIM4-CH3 4-O-6531
MIM4-CH4 4-O-6534
MIM4-CH5 4-O-6535
MIM4-CH6 4-O-6538
MIM5-CH1 4-O-6546
MIM5-CH2 4-O-6549
Table continues on next page
1MRK505222-UUS C Section 17
Station communication
1027
Technical reference manual
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