Cooper Instruments & Systems DFI INFINITY Digital Force Indicator/Controller - Manual (Page 13)

4.7 Full Duplex
Two channels (e.g., two twisted pairs) with bi-directional data flow at any time (one simplex channel in each
direction).
4.8 RS-232 (CCITT V.24)
Bipolar ±5 to ±15 V point-to-point transmission for short distances and moderate data rates. The meter operates
with full-duplex RS-232, with two wires (RX and TX), plus a common ground, to transmit baud in either direction.
A third signal wire, Request To Send, is referenced to the same ground wire and is used by the computer (DTE)
to control transmissions of the meter (DCE).
Receiver sensitivity is ±3 V and impedance of 3 to 7 kilohms. (Although RS-232 is nominally for only one driver
and one receiver on the line, custom high-impedance versions exist for limited multipoint use.)
4.9 RTS
A designator for the “Request To Send” control signal from the computer, carried on a wire separate from that of
the data, and used by the meter to permit or inhibit transmissions in Continuous Mode RS-232. The other
control line of RS-232, CTS, is not used in meter communications.
4.10 RS-422
Unipolar-voltage (3.6 to 6 V supplies) simplex drive of a bus with ±2 V-differential signals (neither wire at
ground) for long distances and/or high data rate. Receiver sensitivity 200 mV, common-mode voltage range ±3
V, and impedance 4 kilohms or more. A maximum of one driver and 10 receivers allowed, with no driver
protection against bus contention. Duplex operation requires another set of hardware.
4.11 RS-485
This is the extension of RS-422 to a half or full duplex bus of up to 32 devices, with multiple drivers and driver-
contention protection. Receiver impedance is now 12 kilohms or more.
4.12 ASCII
Table 4.1 shows the ASCII (American Standard Code for Information Interchange) symbols that can be encoded
in 7-bit binary code (DB0 through DB6). When organized in table form, these 7 bits may be regarded as the
symbol address, the most significant 3 bits determining the column and the last four bits determining the row.
These symbols include all the decimal numerals, letters, punctuation marks, common abbreviations and control
characters, including non-printed symbols such as Carriage Return and Line Feed.
The 7-bit symbol code (or address) is called a “character”, and digital communication with the meter is made
with a string of these characters.
When transmitted, each character is preceded by a start bit (BAUD) and followed by one or two stop bits plus an
optional parity bit, making a train of 10 or 11 baud for each transmitted character. If you are building a system
from the UART up (Universal Asynchronous Receiver/Transmitter), that device must be informed of the number
of data bits, parity, stop bit length, etc., so that it properly decodes the incoming stream into the bytes that your
program can recognize (check the UART or plug-in board literature for required control signals).
As dictated by FORMAT statements, a symbol may be sent by transmitting just its table address (one character,
plain ASCII) or by HEX-ASCII, which uses two characters, one for each of the two hex address nibbles (0
through 7 for column nibble, 0 through F for the row nibble, shown on top and left-hand side of Table 4.1).
4.13 HEX ASCII
Storage in most digital devices is in groups of 8 bits, called bytes. Each byte has a most-significant nibble (the
left most 4 bits) and a least-significant nibble.
CF 125 INFINITY SC GUIDE 9 M1519/N/0605