Black Box ME260A, Owner'S Manual

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24
MODULAR MODEM ELIMINATOR
Timing Modes
When set for operation in the modem eliminator configuration, the Modular
Modem Eliminator offers two timing modes. The selection of the desired mode
is made by an internal jumper:
• Internal (INT) timing: the clock signals for the two DTEs are provided by the
internal clock oscillator of Modular Modem Eliminator. The data rate is set by
means of the front-panel rate selector. In this case, the two DTEs must operate
with external clock.
Figure 2-12 shows the flow of the clock signals in this mode, as well as the flow
of interface control signals.
• External (EXT) timing: the Modular Modem Eliminator accepts an external
clock signal from interface 1 and distributes this signal to interface 2. The data
rate is then determined by the external clock signal. In this case, the DTE
connected to interface 1 must operate with internal clock, and the
DTE connected to interface 2 must operate with external clock.
Figure 2-12. Modem eliminator application.
External Clock
J1 J2
DCE Mode DCE Mode
Internal
Oscillator
DTE
DTE
External Clock
TC
TD
RTS
RC
RD
DCD
DSR
DTR
CTS
FG
SG
RC
RD
DCD
TC
TD
RTS
DTR
DSR
CTS
FG
SG