Revised 08 2021
Drawing No. LP0673
5
RS232 Communications
RS232 is intended to allow two devices to communicate over
distances up to 50 feet. Data Terminal Equipment (DTE) transmits data
on the Transmitted Data (TXD) line and receives data on the Received
Data (RXD) line. Data Computer Equipment (DCE) receives data on the
TXD line and transmits data on the RXD line. The LD emulates a DTE.
If the other device connected to the meter also emulates a DTE, the TXD
and RXD lines must be interchanged for communications to take place.
This is known as a null modem connection. Most printers emulate a DCE
device while most computers emulate a DTE device.
Some devices cannot accept more than two or three characters in
succession without a pause in between. In these cases, the meter
employs a busy function.
As the meter begins to transmit data, the RXD line (RS232) is
monitored to determine if the receiving device is “busy”. The receiving
device asserts that it is busy by setting the RXD line to a space condition
(logic 0). The meter then suspends transmission until the RXD line is
released by the receiving device.
RS485 Communications
The RS485 communication standard allows the connection of up to 32
devices on a single pair of wires, distances up to 4,000 ft. and data rates
as high as 10M baud (the LDA is limited to 38.4k baud). The same pair
of wires is used to both transmit and receive data. RS485 is therefore
always half-duplex, that is, data cannot be received and transmitted
simultaneously.
3.4 SERIAL WIRING
TBD
A
COMM
RXD
TXD
4
2
3
1
B
5
232
485
5
LD METER
RECEIVING DEVICE
+5V
4
47K
47K
3
B (-)
A (+)
COMM.*
Transmit
Enable
* OPTIONAL
Terminal Block Connection Figure
1
1
TXD
RXD
COMM.
LD METER (DTE)
RECEIVING DEVICE
2
RXD
TXD
3
3
2
7
5
5
DTE
3
2
DB9
2
2
3
3
DTE
DCE
DB25
DB25
Terminal Block Connection Figure
4.0 r
evIeWIng
the
F
ront
B
uttons
and
d
Isplay
BUTTON DISPLAY MODE OPERATION
PROGRAMMING MODE OPERATION
PAR
Access Programming Mode
Store selected parameter and index to next parameter
RST
SEL
Resets display
Index display through selected displays
OPERATING MODE DISPLAY DESIGNATORS
MAX
- Maximum display capture value
MIN
- Minimum display capture value
“1” - To the left of the display indicates setpoint 1 output activated.
“2” - To the left of the display indicates setpoint 2 output activated.
Pressing the
SEL
button toggles the meter through the selected displays. If display scroll is enabled, the display will toggle automatically
every four seconds between the enabled display values.
Advance through selection list/select digit position in
parameter value
Increment selected digit of parameter value
The serial connections are made via terminal block TBD located
inside the unit on the left side for the LD2 and on the right side for the
LD4.
