Black Box High Speed COS-4, User Manual

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CHAPTER 4: Operation
Table 4-3. Pinning, Modem to COS (ECM12C Cable*)
Modem COS as DTE
DB25 DB25
RD 2 ----------------------------------- 2 TD
TD 3 ----------------------------------- 3 RD
CTS† 5 ----------------------------------- 5 CTS†
SGND 7 ----------------------------------- 7 SGND
DTR† 20 ----------------------------------- 20 DTR†
*Our ECM12C cable is pinnned this way. It also carries Pin 1, PGND, which the High
Speed COS-4 and COS-8 support but doesn’t require, as well as Pins 4, 6, 8, 15, 17,
and 22 (RTS, DSR, RLSD [DCD], TSETC [TC], RSET [RC], and RI respectively),
which the COSes don’t support at all.
††When a device attached to the COS raises its flow-control lead, the COS sends
the appropriate flow-control signal to the device on the other end of the connection.
For example, suppose a line driver on Port 0 is communicating with a mux on Port 4.
Both the driver and the mux are DCEs, so both ports are set as DTE. When the line
driver on Port 0 raises CTS, the COS raises DTR on Port 4; and when the mux on
Port 4 raises CTS, the COS raises DTR on Port 0. On the other hand, if the device
on Port 4 is a PC (a DTE, so that Port 4 is set as DCE), then when the line driver on
Port 0 raises CTS, the COS raises CTS on Port 4; and when the PC on Port 4 raises
DTR, the COS raises DTR on Port 0.