RX+
RX-
TX+
TX-
TX+
TX-
RX+
RX-
WIRING DIAGRAM
OPERATION:
While the SHM-B Sync and its attached devices are plugged in and turned on, the system should operate continuously
without requiring human intervention. You can, however, monitor the unit's status at any time by looking at the LED's marked
"TD" and "RD" on the unit's front panel. These will indicate the logic status of the transmitter and receiver circuitry,
respectively: They will light green for a "high" logic level or red for a "low" logic level, and will flicker as data is transmitter and
received. (These LED's respond to the actual transmitted and received signals, not the TD and RD lines of the RS-232
interface).
The RS-232 Signals, Flow Control, and Synchronous Timing:
The SHM-B Sync should be connected to your RS-232 device with a standard RS-232 cable. The cable must have a DB25
male connector at the SHM-B Sync's end. The type of connector at the other end will depend on what type of RS-232 device
you're attaching, and the pinning of the cable will depend on whether the device is a DTE or DCE;
1. To connect a sync terminal, a PC running a sync protocol, or another DB25 male sync-DTE serial port, use a
straight-through-pinned DB25 male-to-female RS-232 cable such as our product code ECN25C-MF.
2. To connect a mux's composite port or another DB25 female sync-DTE serial port, use a straight-through-pinned
DB25 male-to-male RS-232 cable such as our product code ECN25C-MM.
3. To connect a sync modem, a mux's channel port, or another DB25 female sync-DCE serial port, use cross-
pinned DB25 male-to male tail-circuit cable such as product code EYN255C.
To implement flow control as soon as the system begins operating, each SHM-B Sync unit forces its own RTS, CTS, DSR,
and DTR signals "High" (above +3V), and as soon as each unit detects the presence of the one at the far end, it also raises
CD in order to signal the attached device to expect data. If the cables are correctly wired and attached, the system is ready
for continuous data transmission.
The control signals will stay in this state unless:
1. One of the SHM-B Sync units is powered down (all signal transmission at its end will cease and the other SHM-B
Sync will lower CD).
2. The 4-wire cable is broken or detached (both SHM-B Sync units will lower CD).
3. An attached device is powered down or lowers DTR or RTS (its attached SHM-B Sync unit will drop carrier and
the other will lower CD).
As far as the synchronous clock signals go, each SHM-B Sync will generate its own internal clock and continuously
transmit it to the attached device on both the Transmit Clock (TC) and Receive Clock (RC) leads while the system is operating.
The SHM-B Sync cannot accept clock from the attached device; it also cannot buffer signals, so it's very important
that the two SHM-B Sync units are set to the same data rate.
Note:
Always keep in mind that both clocking and flow control operate
locally only--the data signals are the only signals passed across
the 4-wire line.
