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CHAPTER 3: Configuration
This chapter contains charts and diagrams that will help you configure your
High-Speed SME V.35:
• Table 3-1 on the next page lists the possible settings of the individual
straps (jumpers) inside the SME. You’ll set these straps to configure some
of the SME’s features.
NOTE
Clock timing is supplied on the SME’s ports in the form of a “send
timing” signal (SCT, derived from that port’s clock source) and a “receive
timing” signal (SCR, derived from the other port’s clock source). Straps
W4 and W5, which determine how the SME gets its clock for each port,
are among those described in Table 3-1.
In the descriptions of these straps, the A position is called “internal,”
the B position is call “recovered,” and the C position is called “external.”
When a port’s timing is internal, the clock is the SME’s internal clock
signal. When a port’s timing is external, the SME gets the clock from that
port’s “terminal timing” (SCTE) signal. When a port’s timing is recovered,
the SME gets the clock from the opposite port’s “terminal timing” (SCTE)
signal.
For most applications both ports’ straps would be set to A (internal
clock). A small number of applications (those in which one device
supplies the timing across the line) would require one strap set to B and
the other set to C. Extremely few if any applications would require both
straps set to C, or one strap set to C and the other to A. The SME will not
work at all if both straps are set to B, or if one strap is set to B and the
other to A.
• Table 3-2 on page 7 lists the possible settings of the data-rate switches S1
and S2 inside each standard SME. Move the positions of these DIP
switches to the setting that matches the data rate used in your system.
• Figure 3-1 on page 7 shows the layout of the SME’s printed-circuit board.
3. Configuration
