In either case, the
handshaking
between the CP-220A and the
Automation
System's
computer conforms to the
RS-232
standard (briefly discussed on
pages 2-73 and 2-74). While the details of
RS-232
communications is
beyond the intent of this manual, the text and the diagram that follow are
meant to provide a basic understanding of the two choices offered by
PARAMETER 54.
RTS
(Request-to-Send) and
CTS
(Clear-to-Send) are the names of two of the
"control lines" that run within the interface cable; they are shown in the
diagram below. These lines connect corresponding points on the CP-220A
and the computer, and if
PARAMETER 54
is enabled, are responsible for
turning the flow of data on or off. In a digital interface like
RS-232
, the
presence or absence of voltages appearing on the "control lines" provide a
"go/no go" signal that is used to control the flow of data.
The following figure depicts the basics of this interface, and labels the
"control" and "data" lines accordingly.
Messages processed by the CP-220A are
transferred to the
Automation System by means
of the
RS-232 cable shown here, and are
carried over the "TRANSMITTED DATA" and
"COMMON" conductors within the cable.
Similarly, data returned by the
Automation
System to the CP-220A is carried over the
"RECEIVED DATA" and the "COMMON"
conductors. The "DATA TERMINAL READY"
and "DATA SET READY" lines are active when
the
Automation System and the CP-220A,
respectively, are operational. Finally, the
"REQUEST TO SEND" and the
"CLEAR TO SEND" lines, the subject of
PARAMETER 54, alternately turn "on" and "off"
to regulate the flow of data between the devices.
CP-220A Central Station Receiver Section 2: Programming the CP-220A Page 2-101
Hook-Up and Installation Manual