olimex lpc2148, gps, uart1

Development Boards MicroMod
1

I am having a slight issue with the ls20031 gps interfacing into uart1 of the olimex lpc2148.

If i interface the gps with a ttl level shifter and go direct to my pc, I can read and configure the gps without any issue.

With that success, I went to interface the gps with the lpc. I added one gender changer in between the level shifter and the olimex serial port.

I am running a serial console on uart0. And that works without any issues. As soon as I plug the gps into the lpc board, with every input/output from the console on uart0, jibberish characters are scattered throughout. They look like this:

->?-?ps`s?ow +]ime /.?//?/ :hr1:0r;1?-KSpemd n???r?ҫ?k?hmsdinw!.//o": ??//…??0?jz00p?00?90

+[kzeo?B?+rv+?R?9??ҫ{??ҫj+Re{}a{}s!/o. z!1 Amtit?eeb//. :j0.980xr9-Lat?udm2… ±?{ ?!0o00?110)yj/100011z?L?Jr??js???:?9)0nr119z0->-±MJ?

I also tried using a USB console and putting the gps on uart0 and the same thing happened.

Is this issue with ttl level shifter and olimex?

2

How close is the GPS antenna to the LPC2148 board? Emanations from the latter might be interfering with the GPS signal.

Leon

3

gps is sitting 4 inches away from the olimex board on the side with the 2 serial ports.

but if i leave in this proximity and go direct from gps to pc, the gps data looks fine.

4

It looks like interference to me, it can be picked up in several ways.

Leon

5

This may seem like a stupid question, but are you using the correct baud rates on both the input/output UART’s?

6

baud rates check out

console on uart0 is 57600

gps on uart1 is 4800

if gps direct into pc, works fine at 4800 (or any speed, I tested)

console works at any speed i setup as well

the problem is when both are running together on the lpc board

7

serial data inverted polarity?

most of the RS232 level shifters invert. so removing it changes things.

as to interference… I have an LPC21xx board with a SiRF GPS with integral antenna that’s on the board, 1-2 in. from the ARM and PCB. Works great.

8

does that imply the serial port on the lpc board is different than a serial port on my pc? or is my level shifter not appropriate for the lpc serial port?

9

ozoney:
does that imply the serial port on the lpc board is different than a serial port on my pc? or is my level shifter not appropriate for the lpc serial port?

no. RS232 defines the voltage levels of mark and space, so your PC must comply with the Standard.

When connecting logic level UART signals (not RS232) between two non-RS232 devices, you need to assure that both devices assume the same data polarity.

10

well it works if going through uext but not through the db9. good enough for development.