2
\$\begingroup\$

I am using a LCD which has RS485 interface. I need to interface with microcontroller (TI piccolo) which has UART lines.

Can I use MAX485 where I can interface DI and RO lines (of MAX485) to UART pins of MCU and A & B (of MAX485) to RS485 lines of LCD?

enter image description here

\$\endgroup\$
7
  • \$\begingroup\$ Can you provide more info on the LCD RS485 interface (like voltage levels?) \$\endgroup\$ Commented Oct 22, 2024 at 17:30
  • 2
    \$\begingroup\$ @VoltageSpike If the LCD says it has RS-485 standard interface, how much you expect the voltage levels to deviate from the standard? \$\endgroup\$ Commented Oct 22, 2024 at 17:49
  • \$\begingroup\$ What are you doing with DE/RE? \$\endgroup\$ Commented Oct 22, 2024 at 18:06
  • \$\begingroup\$ @Justme - if LCD datasheet is saying it is RS485 supported, Can we implement MODBUS protocol for LCD ? \$\endgroup\$ Commented Oct 22, 2024 at 18:08
  • 1
    \$\begingroup\$ "not using DE and RE" ... you definitely need to enable DE or /RE at least some of the time or you won't get any signal through the MAX485 at all ... can you put some information with a link to the LCD datasheet? \$\endgroup\$ Commented Oct 22, 2024 at 21:03

2 Answers 2

Reset to default
3
\$\begingroup\$

Yes, that shouldn't be a problem as long as the LCD has an RS485 interface. For short runs of cable you probably don't even need to provide a termination resistor (but DNL one just in case). The voltage levels of the LCD and MAX485 will need to be matched.

\$\endgroup\$
3
  • \$\begingroup\$ How to match LCD voltage levels ,Can you suggest ? The LCD which I am referring does not have specs mentioning voltages. \$\endgroup\$ Commented Oct 22, 2024 at 17:37
  • 3
    \$\begingroup\$ The voltages do not need to be matched - RS-485 is a standard so either you use standard voltages or it's not RS-485. RS-485 buses use 5V chips like the MAX485. Some chips use 3.3V and are barely but still compatible. \$\endgroup\$ Commented Oct 22, 2024 at 17:48
  • \$\begingroup\$ Just to clarify you do need to match voltages for RO, DI, DE, /RE but these must be compatible with your microcontroller -- I believe Piccolo is a 3V3 device but the MAX485 is 5V. So check datasheets carefully and consider level shifting or a 3V3 driver, perhaps MAX3232 \$\endgroup\$ Commented Oct 22, 2024 at 21:13
0
\$\begingroup\$

If you are sure that the LCD uses RS-485, you have nothing to think about. It will work without any problem. I strongly recommend using a shielded cable, keeping the distance short and using the appropriate termination resistors. Pinout should be;

  • RO -> MCU RX
  • DI -> MCU TX

RS-485 pins are already obvious. A -> A, B -> B

\$\endgroup\$
2
  • \$\begingroup\$ I think there should be some improvements. You mention how TX and RX should be connected, but leave out other important pins. Also why the RS-485 connection should be kept short, and how short is short in some numeric quantity? As RS-485 can go up to 1200 meters, does short mean 120 meters, 12, or 1.2? \$\endgroup\$ Commented Nov 12, 2024 at 20:58
  • \$\begingroup\$ Yes, you are right about other pins. I just indicate most confused pins. DE and RE pins just IOs to handle flow control. About distance you are also right. I mean 1 or 2 meter for test purposes because problems may occur when distance increased. He just need to be sure if it is working on short distance then of course may increase the distance. \$\endgroup\$ Commented Nov 12, 2024 at 21:04

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.