SparkFun Forums

[icbrainy]

Howdy folks,

Does anybody know if the line of serial/i2x/SPI 4-digit 7-segment displays ([url=https://www.sparkfun.com/products/11442]particularly this model[/url]) can be directly driven from an internal RS232 port and if so whether it requires data to be buffered or unbuffered with a small delay between each byte?

Appreciate your expertise!

[Mee_n_Mac]

A true RS232 port will output voltages that go from 3<->15v to -(3<->15)v. The display won't tolerate - voltages.

[icbrainy]

But even if I use this "MAX" 232-to-TTL chip I've been recommended by the tech support guys, would I still need buffer the data as a block or send each byte one after another with a delay in between (i.e. 30-50ms)?

[Mee_n_Mac]

But even if I use this "MAX" 232-to-TTL chip I've been recommended by the tech support guys, would I still need buffer the data as a block or send each byte one after another with a delay in between (i.e. 30-50ms)?

I don't know. You might want to e-mail SFE tech support to be sure.

IF I were coding the display end ... I'd buffer the the incoming bytes to a certain depth and wait to see that the x-missions has stopped before I updated the actual display. The buffer depth would be a tad longer than the max expected given the nature of the display. This is so obvious I can't believe it wasn't done. So I doubt you can send a byte-byte-byte message faster than the spec and have it rejected.

Then, given that data "block" has been sent, how quickly can the next block come (which I think is your real question) ? I dunno. I'd be hard pressed to believe it would take more than 1 msec to process all the data in a block, but that's just my guess.

[waltr]

What you really need to do is put an O'scope probe on the data line. Then you can 'see' the Voltage levels and the data timing.

[icbrainy]

I wish to sincerely apologise about this guys but I just realised that I'm not using a native port and found out that I'm using an older revision of the AXE027 link cable (the variant during the times where the 'PICAXe M' chips where the most recent models). The label must have fell of due to heavy previous use.

Should I just use of these? http://www.sparkfun.com/products/12977
It's not what I had in mind since it adds another port without using an already existing one but I could just route the cable through my project's chassis interior and coil up the unused excess, right?

I don't know. You might want to e-mail SFE tech support to be sure.

I did at the same time when I was enquiring to get a clearer image in my head about TTL and RS232, but I think the person that took on my enquiry must have overlooked that part.

[Mee_n_Mac]

From what I can tell the AXE027 cable performs the same function as the SFE cable you linked to. Both convert USB to 5V TTL serial ... just what the display needs (when you power it w/5V).
http://www.picaxe.com/docs/axe027.pdf

[icbrainy]

Worked it all out, thanks a lot for the assistance.

(Requesting topic lock/archiving)