10
RS-232 DATA SHARERS
2.2 Typical Asynchronous Application
In this kind of application, the devices sharing the line (the “slave devices”)
are usually local intelligent terminals or PCs. The shared line runs from the
RS-232 Data Sharer directly to a controller, processor, or host (the “master”
device). The slave devices must be able to switch the Request to Send (RTS)
signal and wait for the Clear to Send (CTS) signal before sending data. This is
because if a slave keeps RTS high, the Sharer will think the slave is streaming
and deny it access to the line. If you want any PCs or terminals that can’t
toggle RTS to share an RS-232 line, call your supplier. See
Section 4.5
and
step 3 in
Chapter 6
.
Suggested jumper settings for a Sharer in this type of application:
√
Jumper W2 in B–C position (25 ms RTS delay)
√
Jumper W3 in B–C position (RXD Gated Mode)
√
Jumper W4 (4- and 8-Port Sharers only) in B–C position (hardware
prioritization)
√
Timeout-period jumpers in B position (10 seconds)
√
Timeout-signal jumpers in A-B position (TXD only)
Figure 2-2. Asynchronous application—an RS-232 Data Sharer
providing four PCs with access to an async host.
Async
Mainframe
RS-232 Data Sharer-4
PCs with
Communication
Software
RS-232 Lines
RS-232 Line