2-WIRE RS-485 TESTING
USING LOOPBACK OR WITHOUT LOOPBACK
PAGE 6 OF 9
5. If you are checking a RTS Controlled Converter or port: Select Options, then RTS (check
marked) to set the RTS indicator red. If using a Port Powered Converter requiring DTR Hi for
power, make sure the DTR indicator is red, DTR (check marked).
6. Type some characters in the upper window. The same characters should appear in the lower
window. Note that the enter key value will be shown in brackets as <0D>
If data is shown in the lower window when typed in the upper, the Converter or port is working.
Actual signal levels can be checked with a oscilloscope. With no termination, the levels must
exceed 200 mV at the receiver, 4 to 4.5 Volts difference between the Data A and Data B lines is
typical when the Data lines are active. With a dual trace scope in DC coupling mode, with one
channel on Data A, and the other channel on Data B, the two lines can be seen as opposite
levels, when A is high, B is low and vice versa. When the transmitter is inactive and properly
powered, 4 volts of bias voltage between Data B(+) to Data A(-) is typical for B&B RS-485
models without device connections or termination.
USING COMTEST TO CHECK OPERATION WITH 2 CONVERTERS -
models without echo jumper
1. Make the necessary Data A and Data B connections between the two converters, wiring Data
A (-) to Data A(-) and Data B(+) to Data B(+).
If the converter requires a bridge jumper between the TD(A) and RD(A), and another bridge
jumper between TD(B) and RD(B), connect the bridge jumpers. Refer to figures for
Connections - Models Without Echo Jumpers.
2. Start ComTest from your Programs menu under B&B Electronics.
3. Select the Com port number for the first converter.
ComTest will only show Windows based Com ports that are not in use. If another program is
using the port, it will not be available. Please close down any other programs that may be
accessing the port. If another program is using the same IRQ number that port is using, you
will not be able to use both ports at once unless both devices are PCI or USB based.
4. Accept the default baud rate, data bits, parity, stop bits.
5. Start another copy of ComTest and select the Com port number for the second converter.
You will need to be able to open and view both data Windows at once, if only one Window is
shown, you will need to change your Windows View settings.
6. Accept the default baud rate, data bits, parity, stop bits (or make sure the settings match the
first converter port settings. Note: 9600 baud is the default SD (Send Data) control setting for
most B&B Converters.
7. If you are checking a RTS Controlled Converter or port on the first port: Select Options, then
RTS (not check marked) to set the RTS indicator dark. (This will be the port to Receive).
8. If you are checking a RTS Controlled Converter or port on the second port: Select Options,
then RTS (check marked) to set the RTS indicator red. (This will be the port to Transmit
from).
9. If using a Port Powered Converter requiring DTR High for power, make sure the DTR
indicator is red, DTR (check marked) for the either port using this type of converter.
(70 stránky)
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