Si-Tex GPS-5 interface
 

Greetings:

Does anyone have electrical and protocol info for the Si-Tex GPS-5
interface? I connected one of the two data out lines (as traced
from a cable used to connect this GPS to the Si-Tex Nav-Add 7000
Chartplotter) to a PC RS-232 Rx input and using a terminal
emulator program found that the GPS seemed to be talking at
4800 baud, 7-bit, odd parity (as opposed to 8-bit, no parity
as per NMEA-0183 specs). The data stream was either 15 commas
or 7 commas, repeated every second, with no intervening characters.
No antenna is currently connected.

A quick look at NMEA-0183 sentences shows blank data between
commas at certain field positions when no fix is available,
but I didn't see a description of completely empty data and
shouldn't each sentence begin with a dollar sign?

Can anyone verify that the GPS-5 talks NMEA-0183, or that with
no previous or current fix that it would output nothing but
commas?

Thanks,

Michael

Si-Tex GPS-5 interface
 

msg wrote:

Greetings:


snip

Can anyone verify that the GPS-5 talks NMEA-0183,

snip

I should mention that of the two data out lines, only one is
active (toggles), the other seems to be a 'return' and static
at +5V. I will invert the data stream and see if it makes
any more sense.

Michael

Si-Tex GPS-5 interface
 

msg wrote in news:13qo9l9paiau127
@corp.supernews.com:

A quick look at NMEA-0183 sentences shows blank data between
commas at certain field positions when no fix is available,
but I didn't see a description of completely empty data and
shouldn't each sentence begin with a dollar sign?


Anytime there is no data in a data field, you'll see ,, so the reading
instrument can count the commas from the header. NMEA is really a
primitive comma-delineated data field from way back in the DOS days. ,, is
the only way it can show a blank field in a system that counts commas from
the header without screwing up the count and putting the wrong data in the
wrong field at the terminal end.

,, just means "I have no data to report in this field.

HEADER,,,,,,,,,,,
would mean I have no data at all for this function.

Most of the equipment is too stupid to raise a flag and warn you there's no
data. It just simply sits and reads nothing with no explanation at all to
confuse the helmsman. To put in warnings would require us to hire real
programmers during development.

Si-Tex GPS-5 interface
 

msg wrote in news:13qp085j9lmcb77
@corp.supernews.com:

msg wrote:

Greetings:


snip

Can anyone verify that the GPS-5 talks NMEA-0183,

snip

I should mention that of the two data out lines, only one is
active (toggles), the other seems to be a 'return' and static
at +5V. I will invert the data stream and see if it makes
any more sense.

Michael


Wow, that's not good! Most NMEA equipment is non-standard with data and
GROUND! If anyone just "hooks it up" that +5 to ground might destroy it.

Si-Tex GPS-5 interface
 

msg wrote:

msg wrote:

Greetings:


snip

Can anyone verify that the GPS-5 talks NMEA-0183,


snip

I should mention that of the two data out lines, only one is
active (toggles), the other seems to be a 'return' and static
at +5V. I will invert the data stream and see if it makes
any more sense.

Solved; this interface works when the data out pair is connected
to an AC optoisolator (H11AA1) which then drives a 1488. A terminal
program on the PC sees valid 0183 data. The design does not permit
a direct connection to a COM port unlike many other GPS interfaces.

Michael

Si-Tex GPS-5 interface
 

Larry wrote:

snip

Thanks for your reply.

HEADER,,,,,,,,,,,
would mean I have no data at all for this function.


snip

I wasn't seeing the header, just commas. Turns out that the
interface wasn't electrically compatible to the PC's com port
(direct connection is usually a kludge anyway) and required
an opto and 1488 line driver to finally work.

Michael