How long to serial upload data from EEPROM? Max232 necessary?

[GreenLeader]

My question has 2 parts:
1.
I need to estimate how long it would take to upload the data stored on a 24LC256 EEPROM, at various baud rates.
Could anyone help with some rules of thumb?

I don't follow what baud rate really means - seems like it has nothing to do with bits or bytes per second, but more about how many times per second the transmit signal changes level.

2.
I am planning to use a 40X1 to transmit my data to my computer using the hserout commands. The PICAXE manual seems to indicate that a MAX232 chip is needed - is this always the case?
Or can I do this using the same hardware scheme that is used for the PICAXE serial download circuit, except connecting to the hserin/hserout pins on the 40X1?

thanks

 

[Technical]

1) baud is exactly that - bits per second. 2400 is 2400 bits per second if you send a continuous stream (which doesn't actually happen with the PICAXE system as you need some processing to read the eeprom between bytes) (divide by 10 to get bytes as you also need a start and stop bit).

2) hserout doesn't always need a max232 as it can be inverted by the hsersetup command. hserin can never be inverted and so does always needs a MAX232

 

[hippy]

1) baud is exactly that - bits per second.

No, I'm not going to be the pedant who starts the two page discussion on "symbol rates"

As per Technical's calculation ...

                  number of bytes * 10
transfer time  =  --------------------
                       baud rate

So for a 24LC256, 64K bytes at 2400 is around 273 seconds. That doesn't include the extra time involved in reading from the I2C Eeprom or sending the byte. For 64KB that will probably add an extra 32 seconds.

So ball park figures ...

2400 baud : 300 seconds ( 5 minutes )
4800 baud : 170
9600 baud : 100

Using HSEROUT will reduce the 30 second overhead, probably to almost nothing.

 

[GreenLeader]

Thanks - that's not too bad - 100s for each EEPROM. I can live with that.

Presumably I could use hserout and go to 115200 baud in which case I am probably looking at about 10s per EEPROM?

On a separate point - I thought the 24LC256 chip was 256Kbit = 32k x 8bits = 32Kbytes, not 64Kbytes?

 

[Dippy]

He's just checking to see if you read. Yes, it's 32k.

 

[hippy]

That'll be one of those inverse 'fake memory devices' which has more in it than the label says

Yes, I got that completely wrong. Divide times by two for a 32KB Eeprom.