RS485#
This expansion board converts the UART signal from the iLCD Linux panel into half-duplex RS485 differential signaling over a twisted pair of wires. The board also provides access to the mounting holes for a 2 row 24 pin header of the Control Port.
Specifications#
Recommended Bitrate 1)2) |
Maximum |
Isolation |
Supply Voltage |
Delay (Auto mode) 4) |
ALERT on |
|---|---|---|---|---|---|
115.2 kBit |
125 kBit |
1500 V |
5 V |
800 µs |
Logic high |
1) This is the bitrate for which “Auto” mode is optimized. 2) For volume orders this value may be adjusted. 3) Two self-resetting fuses are tripped at higher voltages. 4) In “Auto” mode TX is held in enabled mode for 800 µs after gg idle before it is disabled.
Modes#
RX is enabled by default. Therefore in order to send data, TX must be actively enabled. There are two ways of doing this, Auto and Manual (Pin10/Pin15). These modes are set via on-board jumpers according to the following table:
TX enable |
J1 pos A |
J1 pos B |
|---|---|---|
J2 pos A |
Auto |
Auto |
J2 pos B |
Manual (Pin 10) |
Manual (Pin 15) |
Auto#
By setting Jumper 2 to position A, the board runs in “Auto” mode. This means that TX is automatically enabled whenever a packet is transmitted. TX is disabled after the last bit is sent after a delay of 800 µs as confred via an RC circuit. By default Auto mode is optimized for 115.2 kBit.
Manual (Pin10/Pin15)#
By setting Jumper 2 to position B, TX can be tied to the corresponding pin (pins 10 or 15, depending on Jumper 1). In this mode TX can be enabled via software by setting the pin to logic high.
demmel products RS485 board (DPA-RS485), dimensions in mm
Warning
Due to a production error Version 1 (DPA-RS485-V1) the silkscreen indicating positions A and B of Jumper 1 is reversed. Please ignore the indications on the silkscreen in V1 and instead refer to the positions indicated in this schematic.
3D Model#
Downloads#