Drawing No. LP0673
Revised 08 2021
14
Communication Format
Data is transferred from the meter through a serial communication
channel. In serial communications, the voltage is switched between a
high and low level at a predetermined rate (baud rate) using ASCII
encoding. The receiving device reads the voltage levels at the same
intervals and then translates the switched levels back to a character. The
voltage level conventions depend on the interface standard. The table
lists the voltage levels for each standard.
Data is transmitted one byte at a time with a variable idle period
between characters (0 to
∞
). Each ASCII character is “framed” with a
beginning start bit, an optional parity bit and one or more ending stop
bits. The data format and baud rate must match that of other equipment
in order for communication to take place. The figures list the data
formats employed by the meter.
Start Bit and Data Bits
Data transmission always begins with the start bit. The start bit signals
the receiving device to prepare for reception of data. One bit period later,
the least significant bit of the ASCII encoded character is transmitted,
followed by the remaining data bits. The receiving device then reads
each bit position as they are transmitted.
Parity Bit
After the data bits, the parity bit is sent. The transmitter sets the parity
bit to a zero or a one, so that the total number of ones contained in the
transmission (including the parity bit) is either even or odd. This bit is
used by the receiver to detect errors that may occur to an odd number
of bits in the transmission. However, a single parity bit cannot detect
errors that may occur to an even number of bits. Given this limitation, the
parity bit is often ignored by the receiving device. The meter ignores the
parity bit of incoming data and sets the parity bit to odd, even or none
(mark parity) for outgoing data.
Stop Bit
The last character transmitted is the stop bit. The stop bit provides a
single bit period pause to allow the receiver to prepare to re-synchronize
to the start of a new transmission (start bit of next byte). The receiver
then continuously looks for the occurrence of the start bit. If 7 data bits
and no parity is selected, then 2 stop bits are sent from the meter.
RED LION CONTROLS TECHNICAL SUPPORT
If for any reason you have trouble operating, connecting, or simply
have questions concerning your new module, contact Red Lion’s
technical support.
Support:
Website:
www.redlion.net
Inside US: +1 (877) 432-9908
Outside US: +1 (717) 767-6511
Red Lion Controls, Inc.
20 Willow Springs Circle York, PA 17406
Character Frame Figure
LOGIC
RS232*
RS485*
INTERFACE STATE
1
TXD,RXD; -3 to -15 V
a-b < -200 mV
mark (idle)
0
TXD,RXD; +3 to +15 V
a-b > +200 mV
space (active)
* Voltage levels at the Receiver
