F8 and a GPS -

Gene Heskett gene.heskett at verizon.net
Wed Jul 2 17:26:02 UTC 2008

On Wednesday 02 July 2008, Mikkel L. Ellertson wrote:
>Gene Heskett wrote:
>> My old Garmin 12 (yeah, it has gray hair) has a very dumb serial
>> interface, so I have to use an adapter to make it usb.
>> And there are no intermittent connection problems?
>> Maybe Prolific has quietly fixed that bug in later issues.  Mine are 5 or
>> 6 years old, one I got from the shack, and another I got from Wallies a
>> year or so later.  Both of them have been problems.  I tried to use one to
>> connect to a ups, but every time it dropped the connection, the ups
>> monitor initiated a shut down about a second later.  Several times a day. 
>> That, and glancing over at the roadnav screen while in western Iowa, and
>> noted it showing me in downtown Indianapolis IN for 30 seconds just got to
>> be too much.  I moved one of them to the heyu circuit, that gave heyu a
>> tummy ache & it would segfault & die.  I asked Charles on the heyu list &
>> he said I wasn't the only one having trouble with pl2303's, and he was
>> telling folks to go get the FTDI devices as they seemed to Just Work(TM),
>> and they have, very well, as have the Atmel silicon in a pair of extension
>> cables I use.
>By intermittent connection problems, do you mean that it would drop
>characters? One problem I have run into is where the flow control
>lines are not implemented. If the hardware and/or application are
>set up to use hardware flow control, this can cause data loss. I
>don't know if this is the case here.

In the case of roadnav, the serial speed is about 1/100th the usb speed, so 
there should not even be a need for flow controls.  AFAT pl2303 is concerned, 
in my tests, trying to run a minicom terminal here, to a serial port on a 
TRS-80 Color Computer 3, (aka a coco3) running nitros9, using a 9600 baud 
connection rate, and Chuck Foresberg's rzsz to move files.  With a pl2303 doing 
that adaptation, I could type by hand from either end and see it perfectly.  
Fire up a zmodem transfer, and the data got so scrambled that zmodem eventually 
gave up on a 12 byte file!  The rz implementation on the coco3 actually 
checksums each character as rx'd into the total for a 128 byte packet, but this 
restricts the coco3 to about 700cps.

I tried every flow control method, but with the coco3 acia chip only having a 1 
byte buffer, and the coco3 was exerting the 7 wire protocol (with xon/xoff, 
control is too slow) that I could see on an rs232 sniffer was working, but the 
pl2303 was apparently ignoring.  Conversely, a transfer from the coco3 to here 
got scrambled even though this box takes naps between bytes received.  I could 
only come to the conclusion that the pl2303 was a $40 POS.  Add in its poor 
showing with heyu, roadnav and 2 different UPS's and any reasoning person will 
reach the same conclusion.

Now I've moved an FTDI adapter to that circuit, and while there are errors that 
make rz do resets & restarts on the larger files, it will eventually get the 
file moved with no errors in the file. I think those are because I don't have 
the 7 wire properly configured on the coco3, I believe it is here on this box 
although stty's nemonics nomenclature is a bit foreign to me & the manpage 
quite frankly, is all but worthless. A manpage should have demo cli examples 
for eol translations and for the two 'std' flow mechanisms in common use.  No, 
instead it explains each option in excrutiating detail, taking up 4 or 5 pages, 
which is info overload IMO to me.

Experts at rs232 protocols are, like me at 73, a dying breed, so there are few 
to ask about it in this world, and I might get 1 or 2 fingers used counting 
them in the coco3 world, very scarce and memories are fading.  Since the coco3 
& os9 (a mini unix) precede google by over a decade, googling is not the help 
it could be.

Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Our business in life is not to succeed but to continue to fail in high spirits.
		-- Robert Louis Stevenson

More information about the fedora-list mailing list