Inverting Serial Data without MAX232.
Moderators: David Barker, Jerry Messina
-
- Posts: 33
- Joined: Wed Jul 01, 2009 5:55 am
Inverting Serial Data without MAX232.
Hi,
I'm trying to communicate with a GPS (BR-355 from Global Sat)
I've configured it to send certain NMEA messages (Plain Ascii Strings) at 4800 baud.
I have communicated with other GPSs sending NMEA messages with my program (true, non-inverted) and have checked that this one is compatible with the messages it sends.
It was designed to be plugged directly in to the computer. I want to connect it to my PIC18F2525, but would like to avoid using a MAX232.
I've read the datasheet, and BAUDCON Bit5 should allow me to invert the data. When I change this to either 1 (inverted) or 0 (un-inverted), nothing happens.
When I plug it into the computer, it works, however.
Am I doing something wrong? Or do I need a MAX232?
Thanks in advance.
I'm trying to communicate with a GPS (BR-355 from Global Sat)
I've configured it to send certain NMEA messages (Plain Ascii Strings) at 4800 baud.
I have communicated with other GPSs sending NMEA messages with my program (true, non-inverted) and have checked that this one is compatible with the messages it sends.
It was designed to be plugged directly in to the computer. I want to connect it to my PIC18F2525, but would like to avoid using a MAX232.
I've read the datasheet, and BAUDCON Bit5 should allow me to invert the data. When I change this to either 1 (inverted) or 0 (un-inverted), nothing happens.
When I plug it into the computer, it works, however.
Am I doing something wrong? Or do I need a MAX232?
Thanks in advance.
Looks like a feature list rather then a complete datasheet, though chances are it is operating at +/-5V RS232 voltage levels.
King Snake from the digital-diy.com forums (he also gets around here at SF) recently had a similar issue, and came up with some solutions
If it is using standard RS232 voltages, then you will need some sort of hardware in between, as they operate with -ve voltage levels
King Snake from the digital-diy.com forums (he also gets around here at SF) recently had a similar issue, and came up with some solutions
If it is using standard RS232 voltages, then you will need some sort of hardware in between, as they operate with -ve voltage levels
digital-diy.com - Hobby microcontroller projects and tutorials. Assembly, PICBasic and C examples.
Australian distributor for the Swordfish Compiler
Australian distributor for the Swordfish Compiler
-
- Posts: 33
- Joined: Wed Jul 01, 2009 5:55 am
I just found the datasheet on the GPS.
It specifies that
"
Protocol
Electical Level: Output Voltage Level: 0V ~ 2.85V
Baud rate: 4800 bps
Output Message: NMEA 0183 GGA,GSA, GSV, RMC, VTG, GLL
"
Checking the 18F2525 datasheet - Page 337 - Input High Voltage - D041A/B
It specifies that on pins RC3 and RC4 (serial data rx and tx), the minimum voltage for a "high" signal is 0.7 x VDD (= 3.5V)
So I assume a problem is too a low a voltage on the input?
It specifies that
"
Protocol
Electical Level: Output Voltage Level: 0V ~ 2.85V
Baud rate: 4800 bps
Output Message: NMEA 0183 GGA,GSA, GSV, RMC, VTG, GLL
"
Checking the 18F2525 datasheet - Page 337 - Input High Voltage - D041A/B
It specifies that on pins RC3 and RC4 (serial data rx and tx), the minimum voltage for a "high" signal is 0.7 x VDD (= 3.5V)
So I assume a problem is too a low a voltage on the input?
-
- Posts: 33
- Joined: Wed Jul 01, 2009 5:55 am