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Re: [LUG] TTL serial to RS-232 or USB?


Robin Cornelius <robin.cornelius@xxxxxxxxx> wrote:
On 7 January 2014 16:56, Rob Beard <rob@xxxxxxxxxxxxxxx> wrote:

Looking into it a bit, it seems it has TTL level 3.3 serial. Now I'm far
from an expert on this sort of stuff, but I seem to recall other devices
with JTAG interfaces needing some sort of chip to convert from TTL to RS232.
This made me wonder, would something like a Raspberry Pi would be able to
talk to it?

The RPis serial pins are indeed 3.3V TTL level so you could connect
this directly. If you needed to go to a proper RS232 signalling level
you need something like a max3232 chip which is exactly that a
bidirectional 3.3V TTL to RS232 level converter. NB do not use the
max232 chip as that is a 5V TTL to RS232 level converter.

Its also possible you could rip apart a USB/Serial converter device as
these often have two chips, one for USB handing that just exposes the
RX/TX pins at 3.3v and the other is the level converter chip, so if
you bypassed the level converter chip and connected your 3.3v TTL
serial directly to the USB chips RX/TX pins that should work as well.
Clearly it depends on the exact make up of the converter so you would
need to open one and then look up the datasheet of the chips found to
be sure. I have seen older USB/serial converters that are 5V so check
that too.



Thanks for the advice Robin, do I'm guessing I'll need extra chips then?

I did a search of eBay and found a USB TTL serial cable for 12 quid, might see if I can find a cheaper one from Hong Kong, it's no major hurry to get the NAS working, for now it will make a nice desk ornament. :-)

Sent from my Sinclair ZX Spectrum
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