40x4 LCD interfacing with a 28X

[BjBlaster]

Hi Guys,

Now that I have got my rs232 logger working well, (http://www.picaxeforum.co.uk/showthread.php?t=11681&page=3) I want to add a 40x4 Character HD44780 LCD to the "bus". In other words has someone used a 28X as a serial to parallel lcd driver? The PC would be sending the LCD the text.

I know it's a bit of an overkill for a 28X, but I have one here and it seemed like a good place to start.

I was hoping for a simple 2400 addressing scheme where I could send it say for starting to print on line one: "lcd1,1,This is the text as a string for line 1"
and "lcd2,2" to send it text starting at line two character 2.

Something like that, as most of the serial to parallel converters I've seen to buy will just send what is coming out of the serial port, where as my "rs232 bus" already has traffic (text) on it so I need to be able to get the LCD to listen for it's own code like "lcd1,1" before printing to screen.

Has anyone tried something like this before?

Cheers

Bj

 

[Texy]

I gave it a go with a spare picaxe that I had once, can't remember which, maybe a 14X or a 18X. Only because I didn't feel that the LCD driver chip good value for money at £4 odd. I found that the picaxe was too slow to be of any real use. If you've done any assembler work on a bare microchip pic, then that would be a better approach, IMHO.

Cheers,
Texy

 

[lanternfish]

I agree with Texy. Did the same with a 28X1 and a 4 x 20 LCD. Found that serial was often overwhelmed by delay in outputting data to screen.

 

[BjBlaster]

Thanks for the info, I was prepared to buy something, but nothing I've seen so far let's me address the LCD when "I" want to on a populated rs232 stream - so it looks like I'll have to start playing with the old assembler and icprog! gee talk about rust... I've gotten quite used to the simplicity of picaxes

Bj

 

[hippy]

If I understand correctly you will have a single serial signal which will carry data for one device and also have interleaved data for an LCD. What you want is something which can pull off the data only for the LCD and pass that to the LCD.

That should be possible with a PICAXE but speed is an issue if, while you are handling what is coming in, you miss later data. The 28X1 and 28X2 have high-speed serial which support background receive which will automatically buffer data but even that has its limits.

A lot depends on how much, how often and at what speed you are sending data and data to the LCD.

 

[Janne]

Yes the background receiving feature in X1 and X2 parts is useful. The X2 is preferred though, as you can invert both pins in the hardware serial pins, so you can directly connect it to the computer with the same resistor trick as the download circuit. The X1 can only invert the TxD pin, so it will need a max232 or equivalent to receive from computer.

My last project uses 28x2 to receive serial data from computer directly onto the scratchpad, and then controls 2 servos accordingly. A bit overkill, but to my understanding using the bit banged serial commands (serrxd and serin) would disable the servo pulses.

 

[nbw]

With the X2 parts running at very fast speeds, do they also support faster SER speeds to the LCD? I know the LCDs can be slow, but surely a 16MHz pax with a decent SER speed should be able to write to a 40x4 LCD, unless you're writing tons of characters each second?