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'[PIC:] fast data transmission to a PIC based syste'
2005\02\21@102802 by Palmed GmbH

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face
Hello, Picers,



with a new project I have the problem that I have to transfer 1MB of data
from a PC to a PIC based device, the data have to be stored in a SRAM.



Up to now I only worked with RS-232 at 9600 Baud, but this would result in
endless transmission times.



Has anybody ever realized a fast transmission to a PIC?



I know about the very fast USB, but when using a USB to RS232 converter I
would bring down the speed to RS232 level.



Is there a chance to use I2C? If yes, are there any converters from any PC
port (parallel, USB, whatever) to I2C?



Any help greatly welcome.



Best regards



Peter



2005\02\21@104556 by Jan-Erik Soderholm

face picon face
Palmed GmbH wrote :

> with a new project I have the problem that I have to transfer
> 1MB of data
> from a PC to a PIC based device, the data have to be stored in a SRAM.

So you have some sort of *external* SRAM, right ?
What type ? You can't run faster between the PC and the PIC
then you can write to the external SRAM anyway.

> Up to now I only worked with RS-232 at 9600 Baud, but this
> would result in endless transmission times.

Not "endless", but maybe not as fast as you want...

> Has anybody ever realized a fast transmission to a PIC?

What is "fast" ??

> I know about the very fast USB, but when using a USB to RS232
> converter I would bring down the speed to RS232 level.

Note that the RS232 standard says nothing about the speed, just
the electrical levels of the signals.

> Is there a chance to use I2C? If yes, are there any
> converters from any PC port (parallel, USB, whatever) to I2C?

The most common method to run "fast" to a PC today, is to use
the USB port. Have you thought about using some of the new
flash based 18F's with builtin USB port ?

Jan-Erik.



2005\02\21@104658 by Mike Hord

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> Up to now I only worked with RS-232 at 9600 Baud, but this would result in
> endless transmission times.

To me, the obvious solution is just to up the RS-232 data rate.  If you can do
9600 baud, you can work out 115.2k.  That would bring you down to ~90 sec,
assuming no parity and very low overhead.

If that's still not fast enough, you can probably go higher, to 230400 even, or
possbily higher still, but then you may find troubles with some PCs.  I don't
know.

To get these levels of data transfer, you'll need to start being careful about
picking your clock frequency.  11.092 (I think) MHz is a good one for true
RS-232 speeds; 3.6869 (again, I think; this is from memory) is also good
for 115.2k.  Mouser even sells a 3.68 MHz ceramic resonator for this.

Need faster speeds?  Parallel is (for now) still fairly available.  As are PICs
with full speed USB 2.0 on board.  But then, those are a little more complex
to us, and I frankly don't know enough about them to advise.

Other options include a PCI card that connects to I2C.  Apparently, according
to GMail's ad on the sidebar here, you can get stuff like that from

http://www.i2ctools.com

I can't vouch for them; I've never even visited their site.

Mike H.

2005\02\21@110015 by Alan B. Pearce

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>with a new project I have the problem that I have to
>transfer 1MB of data from a PC to a PIC based device,
>the data have to be stored in a SRAM.

Where is the data going once it reaches the PIC?

2005\02\21@111018 by Mike Harrison

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On Mon, 21 Feb 2005 16:27:35 +0100, you wrote:

{Quote hidden}

The FT232 chip will do up to 3Mbaud (using the D2xx drivers) . Not sure what the overall rate after
USB overhead will be but I would imagine better than RS232's 115K limit.

FT245 may be capable of higher throughput.


2005\02\21@122511 by Wouter van Ooijen

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> If that's still not fast enough, you can probably go higher,
> to 230400 even, or
> possbily higher still, but then you may find troubles with
> some PCs.  I don't
> know.

It will get you in trouble on the PC side only when the PC for some
reason refuses the baudrate. Note that the selected baudrate only
affects the FT232-PIC communication. In a recent project I used 512kbps
(18F running at 40 MHz) without any problem.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2005\02\21@155355 by Jinx

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> Has anybody ever realized a fast transmission to a PIC?

I've an audio product that dumps data from large EEPROMs and
SRAMs to both a PIC and a playback IC. The memory datalines
go into a 74HC251, which is clocked by half a 74HC393. Do you
have to stick with 2 wires or can you use a similar scheme out of
the parallel port ? Maybe 8 data lines into a 74HC165 and Strobe
as the "get byte" signal to the PIC. Or lose the serial component
altogether and run parallel data straight into the SRAM with the PIC
controlling address and R/W, or parallel data into a multi-port PIC

If you want to stick with two wires, maybe put a parallel-serial
converter at the PC end. It can get its power from there too

2005\02\21@191112 by olin_piclist

face picon face
Palmed GmbH wrote:
> Up to now I only worked with RS-232 at 9600 Baud, but this would result
> in endless transmission times.
>
> Has anybody ever realized a fast transmission to a PIC?

Sure.  I use 115200 baud just about all the time.  That's well over an order
of magnitude faster than your 9600 baud solution.


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