Matrix Orbital Corp

Hi Group,

I just wanted to confirm the power connections for the LCD2041 that I have.

I am using an external +5V power supply. It is connected to VCC and GND of the Power Connector (#5, Figure 10, page 8 of Manual).

I have a RS232 cable connected to the DB-9 Connector. (#1, Figure 10, page 8 of Manual). In this case,only pin2, pin3 and pin5 are connected thru.

If I plan to connect to the computer, to check with uProject, should these be my connections:
LCD-end (according to manual) -- Computer-end
pin2 (Rx) -- pin3 (Tx)
pin3 (Tx) -- pin2 (Rx)
pin5 (GND) -- pin5 (GND)

However, isn't the LCD a DCE, where pin2 should be TX and pin3 (RX). Does that change things around?

Also, I read somewhere that if I am connecting it to a serial port of a micro-controller, I need to flip TX and RX around.

Am I on the right wavelength or have I gotten it all messed up?

Thanks!
- PB

Hi PB,

Thanks for your post, it looks like you've found a mistake in the LCD2041 manual. I suppose most people just grab a serial cable, plug the unit in, and don't even think about the connections. However, it looks like Rx and Tx are labeled backwards.

I grabbed an LCD2041 board, and it looks like Tx is pin 2 and Rx is pin 3. Meaning the connections on your end should also be reversed.

LCD -------- Comp
pin 2 (Tx) - pin 3 (Rx)
pin 3 (Rx) - pin 2 (Tx)

As far as the micro controller issue is concerned, I have not heard of flipping the Rx and Tx signals. Just be sure that the controller emulates the computer connections shown above. If need be, you can always play around with the legacy jumpers ('X' & '||') which can do the switch for you.

Finally, if you do throw a controller on the other end, make sure it is communicating at the same level as the display. Many controllers have a TTL output, so scope it out first and make sure you've got the protocol select jumpers in the right place on the display.

I apologize for the confusion in the manual, and can assure you it's on my list of things to fix, and should be remedied shortly. If you have any questions or concerns regarding that LCD2041, just post them here and we'll be happy to answer them.

Thanks,
Troy

Hi Troy,

I was actually making my own serial cable connection - thus the pin issue came up. Thanks for clearing that out.

As for the microcontroller, the port that I am using, uses RS-232 signal voltage levels. Thus, I should not need to change any settings on the LCD or microcontroller, because on the LCD it is Rs-232 by default?

Thanks,
- PB

Hi PB,

No worries, I'm glad you found that issue in the manual; I was just trying to offer some sort of reasonable explanation as to why it hasn't been fixed yet.

If you've got a controller that is communicating at RS232 levels, the default LCD settings will allow for correct communication, so no changes will be necessary

~Troy