SKM53 GPS Module Need Help !!!

[has_mmu]

Hye there,

Currently i am using this product to get GPS value.
http://www.skylab.com.cn/SKM53.html

I already set Uart to receive but nothing coming out.


Here is my setting for Uart: //C18 language
//---------------------RX Uart Setting-----------
SPBRG=31; //9600BPS FOR 20MHZ
TXSTAbits.BRGH=0; //LOW SPEED CONFIG
TXSTAbits.SYNC=0; //ENABLE SERIAL ASYNCHRONOUS
RCSTAbits.SPEN=1; //SERIAL PORT BIT ENABLED
RCSTAbits.RX9=0; //8-BIT RECEPTION
RCSTAbits.CREN=1; //ENABLE RECEPTION
//---------------------RX Uart Setting-----------


unsigned char uart_rec(void){ //receive uart value function
unsigned char rec_data;
while(PIR1bits.RCIF==0);//wait for data
rec_data = RCREG;
return rec_data; //return the received data
}


The default rate for the module is 9600 and i am using 20MHz with PIC18F4550.
FYI i am using SN7407N to convert the 2.8 TTL to 5V TTL.
It got stuck at (PIR1bits.RCIF) Condition...

I am connecting th TX(GPS)---> SN7407N ---->RX(PIC18F4550)
If this project is success, i will share the code for this GPS module.

THanks

[sich]

Hi did you trace your uart output using PC serial port to see whether you're sending the correct data? Usually I use UC00A USB to UART converter to troubleshoot uart problem.

If your terminal program is set to the same uart config as your mcu, you should get the correct result. Otherwise, there's something wrong with the program and/or circuit. If you can get the correct data in terminal program, that means the mcu and uart program is okay. Then the problem lies at the connection part (perhaps, by assuming that the basic circuit is fine)...

[has_mmu]

Hye there,

I checked the connection many times to ensure the connection is correct.
i just want to ask if it is still possible to get data if i stay in my room to program the gps....
I staying in 2 storey house....
FYI i did leave RX(GPS Module) and RST(GPS Module) open and not connected to any port.

Provided is comparison between EB-85A and skm53.
I confuse between the declaration of I/O

Thanks
Madi

SKM53



EB-85A

[sich]

I checked the connection many times to ensure the connection is correct.

What about the software part?

i just want to ask if it is still possible to get data if i stay in my room to program the gps....
I staying in 2 storey house....

Usually the signal is weak indoor...may be can put at the windows.

FYI i did leave RX(GPS Module) and RST(GPS Module) open and not connected to any port.

Leave RST open? I'm not sure about it but since it's Module Reset, you need to give that pin '1' or 'High' or 'pull-up' instead of let it floating (unless it says there's internal pull-up) for it to enter normal running mode.

[FloatingMachine]

The GPS should output the data no matter the GPS signal is locked or not. This means it should ouput the NMEA 0183 sentences as well in indoor.

just like what sich said, try to pull up the RST pin to high and see. If it's still not working, the best way is to look at the Tx pin by using an oscilloscope.

[has_mmu]

The GPS should output the data no matter the GPS signal is locked or not. This means it should ouput the NMEA 0183 sentences as well in indoor.

just like what sich said, try to pull up the RST pin to high and see. If it's still not working, the best way is to look at the Tx pin by using an oscilloscope.

I tried to pull up RST Pin to high(with 10k resistor) but still no data come out.
I measure the voltage of TX(GPS) with multimeter(i dont have oscilloscope) and see there is voltage up and down.
I am sure this is pulses of data.

This module really challenge me.

Any helps/ideas are welcomed.

I included my circuit pic

[shahrul]

What is your GPS output level? I think it's lower than 5V. Did you use logic level converter?
I'm also will interface GPS module in 2 weeks. I see, there is no command need to give to GPS, just PIC read the UART data and analyze it. I think to use logic level converter on sgbotic.com or just use transistor. I'm learning actually,
edited:
Sorry, I did't read all your first post. You are using SN7407 logic converter. This help me..

[has_mmu]

//---------------------RX Uart Setting-----------
SPBRG=31; //9600BPS FOR 20MHZ
TXSTAbits.BRGH=0; //LOW SPEED CONFIG
TXSTAbits.SYNC=0; //ENABLE SERIAL ASYNCHRONOUS
RCSTAbits.SPEN=1; //SERIAL PORT BIT ENABLED
RCSTAbits.RX9=0; //8-BIT RECEPTION '0'=8 bits , '1' =9 bits
RCSTAbits.CREN=1; //ENABLE RECEPTION
//---------------------RX Uart Setting-----------

New founds:
This setting for 8 bit transmission.
The SKM53 GPS module is using 8 bit transmission and 1 stop bit.
So it sounds like it needs 9bits transmission.

Should i read RXD for the 9th bit to check whether the byte is ready to be read?
I will try and see what happens.

Thanks

[shahrul]

New founds:
This setting for 8 bit transmission.
The SKM53 GPS module is using 8 bit transmission and 1 stop bit.
So it sounds like it needs 9bits transmission.

Should i read RXD for the 9th bit to check whether the byte is ready to be read?
I will try and see what happens.

Thanks

8 bit transmission is normal with 1 start bit and 1 stop bit. So, the setting is 8 bit, not 9 bit.

I thinking of your logic converter. If the GPS give signal 3.3V, it should give 5V to PIC and if the GPS give 0V, it should give 0V to PIC. What your converter do (I think the chip same function as ULN2803), if GPS give 3.3V the output is 0V and if GPS give 0V the output is 5V. Then the signal UART have been inverted.

[has_mmu]

I thinking of your logic converter. If the GPS give signal 3.3V, it should give 5V to PIC and if the GPS give 0V, it should give 0V to PIC. What your converter do (I think the chip same function as ULN2803), if GPS give 3.3V the output is 0V and if GPS give 0V the output is 5V. Then the signal UART have been inverted.

I tested the input(pin1) of SN7407N with 2.8V and Output(pin2) was measured as 5V.
If input is 0V the output will be 0V.
and i found the minimum voltage for output to be 5V is about 1.6V.

I think the best way to investigate the problem is by using oscilloscope.

Thanks