Serial cable for dummies :-)

Art · Post by **Art** » Fri May 16, 2008 7:08 am

Can you see the numbers on the chip on the PCB?

kasikeeper · Post by **kasikeeper** » Sat May 17, 2008 3:13 pm

Below are the schematics of the sparkfun rs232 shifter board.

http://www.sparkfun.com/datasheets/Prot ... er-SMD.pdf

I have no clue how it works but I guess 2.5V are not enough to drive the LEDs.

As I said, I can receive packages (although not what I expected e.g. 350 for 'A') but there is no transmitting. Aren't the RX AND TX lines required to perform transfers in any direction anyway (serialization, handshaking etc.) So as I receive something on my PSP, eg 350 for 'A' I can theoretically assume ´that RX and TX work, although no echoing is passed back to my terminal app.

Oh and yes, I use Docklight as terminal program. Can you recommend another one?

Art · Post by **Art** » Sat May 17, 2008 9:31 pm

Odd, you can't really identify the chip on there,
but I can tell you that you that you don't need both Tx & Rx to send data one way.
There's no clock signal, and I've connected serial devices with just two wires
(Rx and Ground).
GPS cables for MapThis also only use the PSP Rx.

I use Tera Term Pro which is a free terminal program.

kralyk · Post by **kralyk** » Wed May 21, 2008 6:05 am

Whats the difference between phat and slim ports?
as I can see the slim one has 12 pins not 6.

Are there just some more for TV out or is it completely redesigned?

peb · Post by **peb** » Mon May 26, 2008 8:07 pm

Peope say max232 is not good for slim because the 1,8v is so litlle for max232 (we can see that in the datasheet too), I haven't slim so I can't try.
but the max232 have brother (I forgive is name) which can work in 1,8-5,5v. So I think it's better to use it.. (I'll edit my post when I find name)

EDIT: his name is max3218.

d1mbu1b · Post by **d1mbu1b** » Wed May 28, 2008 5:07 am

peb wrote:Peope say max232 is not good for slim because the 1,8v is so litlle for max232 (we can see that in the datasheet too),.

The threshold voltage for both 5v and 3.6v ttl is still 1.5 volts.
Like you said, and as you can see in the image the Tx line is driven to about 1.8 volts.

Here is the Tx line of a Motorola T191 serial cable that has the max232 chip built in.

Vcc is powered by an internal voltage supply fed by the DTR and RTS lines that are always high with no flow control. This can be seen in this schematic

*** This means that you don't need to use the +3.3 volts from the PSP!!!!

I bought mine for about 20 bucks with shipping.

The only drawback that I see is that it takes about 12 ms for the device to start operating. If my memory serves, the RC time constant in the schematic is 1 ms that means Vcc should be 99.3% of the way to 5v in about 5 ms, not sure why it takes 12 to start clocking data.

This is a one time delay and all subsequent writes are not affected.

I have not tested the rx side and plan to do so as soon as I get all my PSP parts.

I plan on using a female stereo jack and these parts for the connection to the PSP...

Hope this helps.