Cooper Instruments & Systems DFI INFINITY Digital Force Indicator/Controller - Manual (Page 16)

Figure 6-1. Character Waveform
The rising edge of the start bit of the next character may occur at any time after the end of the last stop bit.
7. CLASSES OF OPERATION
There are two (2) classes of operation associated with meter serial communications: Point-to-point and
Multipoint. (Refer to section 10.19 for Process, Temperature, Strain Gauge and Universal meters and Section
11.25 for Rate Meter, Totalizer and Batch meters.)
7.1 Point-To-Point
No device address is included in the command or response message when operating in this class. There are
two (2) modes associated with this class; CONTINUOUS and COMMAND.
7.1.1 Continuous Mode
For RS-232, the computer can direct the meter to repeatedly transmit the data and status information in the
format specified by the communications setup (which includes a selectable parameter to space out the
transmissions for data logging purposes).
Continuous mode is not used on RS-422/485, because no RTS line is present to prevent bus contention.
However, you can use one meter using a RS-485 board by configuring the meter for point-to-point continuous
mode, and configure it so that it is enabled at all times. This will result in allowing for transmission to be sent for
longer distances to such devices as large remote displays.
Control of the continuous mode is by RTS level. Either message or character control can be specified. In the
former case, RTS polarity is checked by the meter before a message is begun, but, once started, the
transmission continues to the end of the specified message. In the latter case, RTS polarity is checked before
each character transmission, so that the meter message can be interrupted after any character.
The specified data and status are transmitted for each new measurement (if so requested), provided that the
selected baud rate and message length are adequate. If the message transmission takes longer, complete
messages are sent as fast as possible, skipping any readings overlapped by a message transmission.
7.1.1.1 Message Handshake
The RTS line from the host controller is checked when the device is ready to send measurement data. If the
RTS is true, it sends the complete message data without interruption eve if RTS goes false in the middle of
transmission. If RTS is false, it skips sending the data completely and continues with the next measurement.
7.1.1.2 Character Handshake
The device checks the RTS input before sending each character and sends characters only while RTS is true. It
always completes sending the data before transferring the late reading to the output buffer.
7.1.2 Command Mode
In this mode, no handshake line is used, but instead a simple command from the host requests that the device
transmit its latest measurement message.
CF 125 INFINITY SC GUIDE 12 M1519/N/0605