B&B Electronics 485TBLED User Manual
485TBLED-0812-1/3
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Model 485TBLED
RS-232 to RS-485 Converter
The 485TBLED converts unbalanced, full-duplex RS-232 signals to balanced, full or half-duplex RS-422 or RS-485
signals. RS-485 is an enhanced version of the RS-422 Standard. It allows multiple drivers and receivers on a two-wire
or four-wire system.
The RS-232 port, configured as a DCE port, has a female DB25 connector with pins 2 (TD input), 3 (RD output), and 7
(Signal Ground) supported. Pins 4 (RTS) and 5 (CTS) are tied together, and pins 6 (DSR), 8 (CD), and 20 (DTR) are
also tied together. Pins 1 (Frame Ground) and 7 (Signal Ground) are connected straight through to the RS-485 terminal
blocks. The RS-485 terminal blocks support Transmit Data (A-) and (B+), Receive Data (A-) and (B+), Frame Ground,
Signal Ground, and +12 VDC input. See Schematic.
signals. RS-485 is an enhanced version of the RS-422 Standard. It allows multiple drivers and receivers on a two-wire
or four-wire system.
The RS-232 port, configured as a DCE port, has a female DB25 connector with pins 2 (TD input), 3 (RD output), and 7
(Signal Ground) supported. Pins 4 (RTS) and 5 (CTS) are tied together, and pins 6 (DSR), 8 (CD), and 20 (DTR) are
also tied together. Pins 1 (Frame Ground) and 7 (Signal Ground) are connected straight through to the RS-485 terminal
blocks. The RS-485 terminal blocks support Transmit Data (A-) and (B+), Receive Data (A-) and (B+), Frame Ground,
Signal Ground, and +12 VDC input. See Schematic.
LEDs
The 485TBLED has two LEDs: a Transmit Data LED to show when the RS-485 driver is enabled and a Receive Data
LED showing data appearing at pin 3 of the RS-232 port. These are very useful for determining if data is getting through
the converter. Note that the TD LED indicates that the RS-485 driver is enabled. Data must be present on pin 2 of the
RS-232 side for data to be transmitted out of the RS-485 side. If no data is present, no data will be transmitted even
though the TD LED is illuminated.
LED showing data appearing at pin 3 of the RS-232 port. These are very useful for determining if data is getting through
the converter. Note that the TD LED indicates that the RS-485 driver is enabled. Data must be present on pin 2 of the
RS-232 side for data to be transmitted out of the RS-485 side. If no data is present, no data will be transmitted even
though the TD LED is illuminated.
Flow Control
The 485TBLED uses two different methods to enable the RS-485
driver, either by toggling Request to Send (pin 4) of the RS-232
side, or by automatic sensing of the data on Transmit Data (pin 2)
of the RS-232 side. This option is user selectable by setting push-
on jumpers located next to the terminal blocks. See Fig. 1.
Removing both sets of jumpers completely can also constantly
enable the RS-485 driver and receiver. This makes the
485TBLED act like an RS-422 converter.
driver, either by toggling Request to Send (pin 4) of the RS-232
side, or by automatic sensing of the data on Transmit Data (pin 2)
of the RS-232 side. This option is user selectable by setting push-
on jumpers located next to the terminal blocks. See Fig. 1.
Removing both sets of jumpers completely can also constantly
enable the RS-485 driver and receiver. This makes the
485TBLED act like an RS-422 converter.
Baud Rate
There is a timing component on the converter, a resistor R9, see Fig. 1. This component is part of the automatic
sensing circuit, and affects the baud rate at which the converter can be used in a two-wire setup. This component, is
factory selected to allow the converter to run at 9600 baud or higher. With this component, the RS-485 driver will shut
off approximately 1ms after the last character has been sent. If you need to change the 485TBLED to a baud rate other
than 9600 baud, you can change this component. To change the baud rate, remove R9 and add through hole
component R14, see Table 1.
Figure 2 shows how to interconnect two RS-485 converters using 4-Wire and 2- Wires.
sensing circuit, and affects the baud rate at which the converter can be used in a two-wire setup. This component, is
factory selected to allow the converter to run at 9600 baud or higher. With this component, the RS-485 driver will shut
off approximately 1ms after the last character has been sent. If you need to change the 485TBLED to a baud rate other
than 9600 baud, you can change this component. To change the baud rate, remove R9 and add through hole
component R14, see Table 1.
Figure 2 shows how to interconnect two RS-485 converters using 4-Wire and 2- Wires.
Figure 2
Figure 1