----- Original Message -----
From: "Philip Galanter" <pg1@ACF2.NYU.EDU>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, October 22, 2001 6:55 AM
Subject: [EE]: I2C EEPROM - fastest, biggest, baddest is ???


> Hi all.  Another beginner question.  Still thinking about
> alternatives to the ISD analog sound chips.
>
> Read about the I2C serial interface and am starting to understand it.
> But wondering if I2C EEPROM's are too small to use to store sampled
> sound.  Are these available in 1 MB or larger?  Vendors/part #'s?
> How many bytes per second can be read if the microcontroller is doing
> little else?
>
> thanks!  Philip
>
> --
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>

The company I used to work for made telephony cards that had voice recording
and playback features.  We used CODEC chips to compress and de-compress the
voice, and then stored it on SPI FLASH chips.

You specifically requested I2C and EEPROM.  Our chips were SPI and FLASH.
The part number was Atmel AT45D041.  The SPI does a 10MHz clock rate max.
The AT45D041 is a ~4megabit part.  The flash pages are slightly bigger than
256bytes.

We chose them because at the time (bout 2 years ago) they were cheapest per
unit storage.  They were AUD$7, which is about USD$3.5 now.  Atmel didn't
have a fab so they were hard to get, but with the economic downturn supply
should be easy now.

As for speed, I vaguely remember calculating something like 50kbyte/s write
speed.  The big bottleneck is your processor.  We used a Motorola 68??? (i
forget which, it had built in ISDN interfaces).  The problem is that you
have to *POLL* the SPI interface of the processor (no interrupt,
inefficient).  Plus, it's buffer is only 1 byte, so the overhead of
reading/writing streams is very large.  You will have the exact same problem
with the PIC.  No matter how fast the FLASH chip is, SPI interfaces in PIC's
and CPU's are designed for reading real-time-clocks, not streaming lots of
data.

If you are only doing one channel of sound, and not much else in the mean
time, you will be ok.  Unfortunately for us it wasn't ok and the company is
now broke after lots of mistakes like this.

But anyway, look at Atmels serial dataflash.  They are basically the
cheapest.

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