Rohde & Schwarz RTE Series - Page 781

Protocol analysis
R&S
®
RTE
781User Manual 1326.1032.02 ─ 20
"= (equal)"
The equal operator (represented by the "=" sign) defines a pattern for
the cell to match. Valid condition entries are characters that match the
cell's defined Numeric Format, Bit Order, and Bit Count. In binary for-
mat, for example, valid characters are "1", "0", "H" (high), and "L"
(low).
Three cases have to be distinguished (cases A, B1, and B2),
depending on the presence of a Variable Length Array: [] in the same
frame description:
●
Case A: If there is no "Variable Length Array" cell, then each cell
marked with the equal operator acts as a key to identify a frame
type. Only if all these cells match up with the expected value, the
frame type is identified.
●
Cases B1 and B2: If there is a "Variable Length Array" cell, then
the equal operator has two different functionalities, depending on
the position of the equal-operator cell within the frame description:
– B1: If the cell is located anywhere before the "Variable Length
Array" cell, the condition acts as a key to identify a frame type
(as in case A).
– B2: If the cell is located immediately after the "Variable Length
Array" cell, the condition acts as an array delimiter.
(Note: If the cell, which is marked with the equal operator, is
located after the "Variable Length Array" cell, but not immedi-
ately after it, the decode result is unpredictable.)
Typically, Manchester protocols use code violations for synchroniza-
tion. The states "H" and "L", supported by the equal operator in binary
Numeric Format, mark that a transition is expected at this bit, but only
a high or low signal is found.
Examples for the MVB protocol:
Master - Delimiter: "=1LH0LH000" (also shown in Figure 13-77)
Master - Delimiter: "=1LH0LH000"
Slave - Delimiter: "=0000LH0LH"
For more details on the violation symbols "H" and "L", see Chap-
ter 13.14.1.1, "Special features of Manchester coding", on page 767.
Also, the length of the pattern must correspond to the bit field length
(or the results are unpredictable).
Custom: Manchester / NRZ (option R&S RTE-K50)M