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18 — RS-232 DCM
18-8 2902 MainStreet Technical Practices
90-2906-01 May 2002
Figure 18-1 Transmit and receive clocks
The two parameters for configuring clocking for synchronous transmissions are:
•
transmit clock source
•
type of synchronous clocking
Transmit clock source
Table 18-2 explains the clock sources for DCE and DTE circuit genders.
Table 18-2 EIA/TIA-232 clock sources
Type of synchronous clocking
When you configure the type of synchronous clocking, you define the effect the
2902 MainStreet system has on clocks passing through it. The type can be set:
•
to the timing of the 2902 MainStreet system (LOCKED) (default)
•
to be passed through transparently (INDEPNT)
Receive clock
The receive clock on RS-232 DCMs with revision 2 DRAGA can be inverted. The
default is no inversion. Receive clock inversion can compensate for a phase shift
between the transmit clock and receive data signals, if it occurs.
Transmit data
Receive data
DTE
data
device
DCE
data
device
Transmit clock
Receive clock
1535
Clocking source Meaning
DCE
External The user equipment provides the transmit clock.
Slave The circuit extracts transmit clock timing from the data stream.
DTE
Internal A baud rate generator on the DCM provides the transmit clock. The baud rate
generator is locked to the system timing.
External The user equipment provides the transmit clock.
Slave The circuit extracts transmit clock timing from the data stream.