I've actually never had a problem with a Prolific based adapter either,
but I know that it is a real problem anyway.
Pick any random cable purchased off amazon or ebay, and it might or
might not be garbage, until you prove it by actually using it.
I've bought probably 20 or more if you count both work and hobby stuff
over the last 15-20 years, and they've all actually worked ok, but that
is just luck. The bad ones do actually exist, and they look just like
the good ones, unless you stick to a few name brands.
And it's also a real thing that even when you have a "good" one where
the chip isn't counterfeit, the chip and the driver even at their best,
still lacks certain features that matter.
John Hogerhuis has explained before (maybe on the fb list instead of
here) that the Prolific interface doesn't allow you to avoid a certain
amount of usb buffering, which can screw up the timing of signals, and
can prevent flow control from actually working, because the flow control
signal itself is queued up and sent only when the next packet is full
and ready, and by then you may have already overrun the M100's receive
buffer etc.
That's the kind of problem that isn't disproved by simply having the
good luck to not have hit it yet.
It's still there and will still hit someone else under some other
condition, or may still hit you tomorrow even if it never has before,
because it's dependent on variables and variable conditions and usage
pattern.
In the specific case of TPDD emulation, I think you can actually get
away with Prolific, and a total lack of flow control, because of the way
the TPDD protocol happens to work. It works in fixed small size packets,
where the entire packet fits inside the M100 receive buffer, and, you
only ever get one packet at a time because the TPDD doesn't send a new
packet until after the M100 sends an ack after ingesting the previous
packet. So the tpdd protocol implements a flow control itself, instead
of relying on the underlying serial channel to be doing that right. So
it's another way you can think there is no problem when there still is.
Or, there is no problem *only* as long as you only keep using it for
exactly that one purpose which happens to work.
--
bkw
On 4/5/19 12:31 PM, Jonathan Yuen wrote:
Hello All,
I've used a prolific usb-serial cable to connect my laptop to a raspberry pi
and it didn't have any handshaking at all, just tx, rx, gnd, and a constant 5V
to power whatever (like the pi itself). This wasn't real rs-232, just the ttl
level serial commmunication, but the pi wanted ttl, not real rs-232.
[email protected]
---
När du skickar e-post till SLU så innebär detta att SLU behandlar dina
personuppgifter. För att läsa mer om hur detta går till, klicka här
<https://www.slu.se/om-slu/kontakta-slu/personuppgifter/>
E-mailing SLU will result in SLU processing your personal data. For more information
on how this is done, click here
<https://www.slu.se/en/about-slu/contact-slu/personal-data/>
