MatrixOrbital LK204-25 / MAX233A / BS2 connection

Ron Czapala

I have·a LK204-25 Serial LCD with a·RS232·D-sub connector. The protocol solder jumpers are set for RS232 (rather than TTL or I2C).

I want to preserve·the current·LCD configuration but have the option of using it with a BS2 by using a MAX233A driver. I have the MAX233A socketed on a small PCB with connections for both·RX/TX·pairs and have no problem using it to connect to the PC.

Even thought the LCD is setup for 9600 baud, I can't get it to function with the MAX233A (it works when connected to the PC serial port with a straight-thru serial cable).·

Here is the wiring scheme:

LK204-25__________________ MAX233A___________ Basic Stamp

---

RS232 || TTL

---

DB9 pin 2 (RX)··<-- pin 18 (T2out) || pin 1 (T2in)···· <-- Serout

DB9 pin 3 (TX)··--> pin 19 (R2in) ..||. pin 20 (R2out) --> Serin

http://datasheets.maxim-ic.com/en/ds/MAX220-MAX249.pdf (Figure 11)

I tried swapping the D-sub RX/TX pin2/pin3 wires with no sucess.

Any suggestions?

Thanks!

Andy Fox

Do you also have a common ground between the LCD and MAX232A? Another thing to check is that the baud rate setting you are using in your SEROUT statement matches the model of stamp you are using. I've interfaced with a Matrix Orbital VFD display through a MAX232 with no worries.

Ron Czapala

Andy,
····· Thanks for your suggestions. I have it working now. I thought I had swapped the TX/RX DB9 pins coming out of the MAX233A but didn't.

I tried it again and everything works perfectly...

It should be like this:

LK204-25__________________ MAX233A___________ Basic Stamp

---

RS232 || TTL

---

DB9 pin·3 (TX)··<-- pin 18 (T2out) || pin 1 (T2in)···· <-- Serout

DB9 pin·2 (RX)··--> pin 19 (R2in) ..||. pin 20 (R2out) --> Serin

NOT THIS

LK204-25__________________ MAX233A___________ Basic Stamp

---

RS232 || TTL

---

DB9 pin 2 (RX)··<-- pin 18 (T2out) || pin 1 (T2in)···· <-- Serout

DB9 pin 3 (TX)··--> pin 19 (R2in) ..||. pin 20 (R2out) --> Serin

Andy Fox

I've done the same thing