Hey guys..
Was wondering if someone could verify my pinouts. I'm using a MAX233 chip to do the conversion from RS232 to TTL. The tech doc is here. It's on page 21.

Since I'm only using one set, and this chip handles two, I have TX from the Empeg going to pin 4, RX on the Empeg to pin 5. Then the VFD is connected via RX from the VFD to pin 3, and TX from the VFD to pin 2.

However, I'm 'fraid that I may have messed up, or the schematic of the chip may be wrong. (There is one glaring error on the diagram already..)

In either case, the PCB's almost done, having a problem getting data to it, now.

Me.

Looks okay to me. What's the glaring error on the diagram? I've not used the 233 much but from what I remember, the example circuit is pretty much what you use.

Looks okay to me. What's the glaring error on the diagram? I've not used the 233 much but from what I remember, the example circuit is pretty much what you use.

Shoot, that's what I was afraid of. It looked good to me, too..
(The error is the fact that the chip is labeled as having 3 outputs, and only one input.)

Me.

Ohh I was looking at the pinout and the wiring of the chip itself
Do you have an oscilloscope or logic probe? You could probably connect a LED and resistor to the pins and see if you can detect any blinking.

Yeah, that was my next step. I have a logic probe, back out in Colorado, which means I gotta pick up another.
I just hope that, at worst, the chip is dead for whatever reason, and NOT the display.
What I'm scared about is when the display gets power, I don't see any of the 'heater wires' (I forgot what they're really called) that seem visible on the Empeg's screen in darkness...

Me.

Assuming this is your K610a, it may not have the filaments since it's not your typical kind of VFD... I don't really know, but it sounds logical enough

Oh, thanks.
The chip, I can replace, not a problem; which, right now, is just about all it can be. (Or a back ribbon cable crimp.).. I just want to leave work NOW instead of i=in 5 hours so I can get a logic probe.

Thanks!
Me.

You got a schematic handy?

I will shortly, actually.

Got my logic probe, and now I'm even more confused...

Without my chip inline, when I send something across the serial line, both the TX *AND* RX lines "pulse". (I was always under the thought that only the RX line would go high.) This lines are normally low, and pulse high.
Slip my chip in, and still TX/RX RS232 lines go high when I send a character, and I also get a pulse on the TTL line (normally high, pulse low). So, I THINK the chip's good. (Gotta verify now, make sure the ttl pulse is coming out on the expected pin..) Which now it's up to my ribbon cable..

Me.

So if you send a character from the PC, both TX and RX lines have activity?
And when you have the MAX233 chip in, the TTL line also has activity?
Does the VFD expect inverted TTL level RS232 or noninverted?

Might be a stupid question but have you checked your wiring and handshaking on the serial plug?

Okay, since I don't have schematics yet (awaiting for 'em..), here's what I got.. Serial cable coming straight out of back of PC. (All this is done on PC. Haven't touched empeg yet) Port IS set at 11920/8N1, which is default for the VFD.
The lines are not shorted together when the cable is plugged in/unplugged...

Thru the ribbon cable (despite what I just said earlier, finished more tests) does convey my signals, including the +5Vdc.

I'm thinking that maybe I need to have the "/RES" line on the VFD connected to the +5Vdc. The sheet for the VFD specified that the VFD will reset when a low level signal is applied to the "/RES" line.

Because as it stands, everything SEEMS to be working, except the VFD ain't turning on..

Whee. Once I figure this little thing out, they're up for sale. (And this is probably something real easy for someone who actually does this everyday. I barely know what I'm doing. Honest. <g>)

Me.

Oh, yeah, don't leave the reset pin floating.

The usual thing to do with these is to tie them to +5 through a resistor (say 10k), and also to ground through a capacitor - 5nF should give you a 50-100 ms reset pulse when power is turned on.

You could try it. It all depends on if the VFD has pulldown resistors on the /RES line. Connect it to 5V with a 10K resistor.
Actually, does the VFD need to be reset everytime you turn it on?

Hmm.. okay, thanks guys.
That cap - does it have to be a specific kind? (Polarized, ceramic..?)

I'll give it a shot as soon as I get outta work, see what I can do..

Thanks!
Mike.

Without my chip inline, when I send something across the serial line, both the TX *AND* RX lines "pulse".

Is the VFD connected when this happens? It does send some stuff back to the host sometimes, maybe it's sending 'E' because you're writing stuff while it knows it's off.

I'm thinking that maybe I need to have the "/RES" line on the VFD connected to the +5Vdc. The sheet for the VFD specified that the VFD will reset when a low level signal is applied to the "/RES" line.

It does suggest (by the drawings) that it's supposed to be driven high, with no connection it may be floating and being interpreted as ground, so the display constantly resets. Or since it's not specified in the..generous..4 page spec sheet, it may not even turn on at all until it sees /RES high for the first time after power is applied.

Actually, does the VFD need to be reset everytime you turn it on?

Not besides /RES needing to be interpreted as high... it automatically initializes itself to a consistent basic state when it turns on.

Schweet!!

I GOT IT! Muhahaha!

The 'docs' for the display say that you have to connect "Host Busy" to "Module Busy" for "SPI communication". In really small print, at the bottom of the page.

Once I hooked those together, everything was kosher! I GOT LIGHT!!

Me.

SPI isn't RS232 though It's a serial bus but not RS232. Must be a mistake on the spec sheet or something.
Good to hear you've got it all working though.

That's what I thought, too...
I was checking some of the pins, and noticed that after a certain number of characters, the "MBusy" was going high, and staying there. So, that's when I noticed the note about that signal, and decided to pop the two together. As soon as I did, all the characters that I THOUGHT were there appeared. So, go figure.

Me.