serial chip issues

trying to use an lcd from 18x using the serial chip (ihave two brand new ones). cannot even get welcome message up on display, in fact, connecting VDD from lcd to pin 18 on serial chip will not even power up display. wiring on breadboard appears correct, (checked several times) and 18x is ok. tried 3 different crystals to no can i prove the serial chips?
Hi Kev,
if you have checked and re-checked the wiring the problem is probably down to either the 10k pot being adjusted incorrectly or that the supply voltage is incorrect. Are the pinouts of the lcd same as on the lcd datasheet ?


Senior Member
Which LCD approach? The Rev.Ed one needs 5.5V & nothing shows on it unless this supply is provided,or a PCB diode is bypassed! Tried SERTXD ? Tried Hyperterminal etc? Stan
Power supply certainly is critical. Use a good 5v supply. 4.5v probably won't be enough.
Adjust the contrast so that black rectangles just begin to appear. Once you get to that point, at least if anything does get correctly sent, you at least know that it will be displayed and that problem is not simply having the contrast too low.
thanks for your replies...the contrast on the lcd is correct, i can power it direct from the supply and i get a line of black squares, supply voltage is 5.57v and lcd pinouts are compatable as per data sheet. I think either the serial chips are duff, fried(cant think of how i done that), or even blank pics and not programmed
theres definitely an issue with the serial chip, it just sits there and does nothing, no output from pin 18 and no welcome message. maybe i will try to drive the lcd directly from the 18x as ive got the spare outputs, just not sure ive got the memory space and the know-how to do the code
Are you using a crystal or resonator?
A resonator is a three pin device and must have the centre leg connected to 0v.
The "optional" reset circuit MUST have a pullup resistor fitted to pin4.

No oscillator will mean the chip does not run and hence will never assert pin 18.

It is always possible to have a DOA chip but to have two is such a remote possibility that it's not worth considering. It is going to be something very simple that may have been overlooked.

At this stage, I would completely disconnect the LCD. Power up just the serial chip and measure the voltage on every pin. In particular, pins 4,5,14 and 18 wrt supply 0v.

Is your LCD backlit?
If yes, then connecting the LCD Vdd to pin 18 will not work. The current drawn by the backlight will be more than pin 18 can supply and may well destroy that output if not the entire chip.
A backlit LCD must have Vdd connected directly to supply.

Edited by - beaniebots on 16/08/2007 10:53:26
i do agree that to have two chips DOA is extremely rare. the backlight is separately supplied on pins 15&16 of the LCD. it is a resonator that im using with centre pin connected to 0v, (my terminology error)).
i will try disconnecting the LCD and measuring the output on said pins when i return work at the moment using their pc.
many thanks for your help


Senior Member
I've had a lot to do helping with Picaxe LCD driving over the last (- gasp- !)4 years & have found by frustrating experience that the LCD at the far end is not always the normal reliable Rev.Ed kit that was initially assumed.Argh! Please hence specify EXACTLY what you are using,with perhaps a pix,schematic & driving code, detailing supply voltage etc as well. We can not read your mind!

Just what is this <i>&quot;trying to use an lcd from 18x using the serial chip - I have two brand new ones &quot; </i> ? The 18X will drive a Rev.Ed LCD kit directly without any &quot;serial chips&quot;. Have you popped in a MAX232 as well ?? The surest way to test your Picaxe is to of course send some serial out to a PC running a terminal program such as Hyperterminal,or (even easier) use SERTXD &amp; F8. Stan

Footnote: Aside from the Rev.Ed kit,there are several other recognised Picaxe LCD approaches,with those of both Peter Anderson &amp; Hippy being highly thought of.

Edited by - manuka on 16/08/2007 11:49:59
many thanks for all replies, i have one duff serial firmware chip which is the one tried first, upon swopping for the other, i think i took out the duff chip and refitted it again instead of replacing it, hence thinking that both chips were duff as i couldnt find anything else wrong. all works fine with the second chip
how daft is that??