Red Lion GEMINI 33 - Manual (Page 27)

TROUBLESHOOTING GEMINI SERIAL COMMUNICATIONS
If problems are encountered when trying to get the Gemini(s) and host
device or printer communicating, the following checklist can be used to help
find the solution.
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 is 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 3300 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 3300 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.
2. Set the Gemini’s unit address to 15 (set switches 7-10 of the Serial DIP
Switch in 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 B 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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