Red Lion GEMINI 2 - Manual (Page 30)

TROUBLESHOOTING GEMINI SERIAL COMMUNICATIONS
If problems are encountered when trying to get the Gemini(s) and host device or
printertocommunicate,thefollowingchecklistcanbeusedtohelpfindthesolution.
1. Check all wiring. Refer to the previous application examples and use them as a
guide to check your serial communication wiring. Proper polarity of all
Geminis and other peripherals must be observed. If a multimeter or ammeter is
available, insert it in series in each Serial loop and check for current flow with
all units powered up. If no current is flowing, either the loop is not wired
correctly, or some other fault has occurred. If too much current has been sent
through a Serial Input or Output, the unit may have been damaged. If a Gemini
is suspected, it can be tested for operation by using the Serial Loop-back test
described in the next section.
2. If the Gemini is set-up with a “host computer”, device or printer, check to make
sure that the computer or device is configured with the same communication
format as the Gemini. The only communication format the Gemini will accept
is; 1 start bit, 7 data bits, odd parity, and 1 stop bit.
3. Check the baud rate settings and make sure all devices in the loop are set to the
same baud rate.
4. Check the Gemini’s unit address. If the Address command is not used when
transmitting a command to the Gemini, the Gemini’s address must be set to 0. See
“Sending Commands & Data to the Gemini” section for command structure.
5. If two-way communications are to be established between the Gemini and a
computer, try getting the computer to receive transmissions from the Gemini
first. The Gemini’s “PRINT REQ.” terminal can be used to initiate the
transmissions from the Gemini.
6. When sending commands to the Gemini, the * (2Ah) must terminate the
command. NO CARRIAGE RETURNS (0Dh) OR LINE FEED (0Ah)
CHARACTERS SHOULD BE SENT TO THE GEMINI. If they are sent, the
Gemini will not respond to the next command.
7. For applications where 1200 Baud or lower is used, the command terminator (*)
can be sent before the string to eliminate any illegally transmitted characters.
SERIAL LOOP-BACK SELF-TEST
The Gemini 2000 has a Serial Loop-back Self-test feature. This test enables the
user to verify the operation of the Gemini when problems are encountered trying to
get the Gemini and “Host device” communicating. In this test, the Gemini’s Serial
Input and Output Loops are connected together with the 20 mA source supplying
the loop current. The Gemini then transmits data “to itself”. If the data is received
properly, the Gemini 2000 will change its Scale Factor value to 0.1111. To perform
the loop-back test, follow the test sequence as described below.
1. With the unit powered down, wire up the serial terminal block, “TBD”, as
shown in the diagram below.
2. Set the Gemini’s unit address to 15 (set switches 7-10 of the Serial DIP Switch
to the down position).
3. Apply power to the unit. On power-up the Gemini will perform the loop-back
test. To check the results: Call up the Scale Factor value by pressing the “3”
key. If the Serial loop is functioning properly the Scale Factor value will be
0.1111. If this result is not obtained, double check the connections with those
shown in the diagram, and the unit address switch positions and repeat step 3.
4. If the connection between the Print Request terminal, “PRINT REQ.” and
“COMMON” is disconnected while the unit is under power, the Scale Factor
value will change back to its previous setting.
If the unit does not pass this test, contact your local Red Lion Controls
distributor.
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