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Need clarification: Hardware UART and P1.1/P1.2


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Hi,

 

I am new to the whole world of microprocessors and just playing around with my Launchpad v1.5 with the MSP430G2553 for a while.

 

I got the UW UART up and running so far, using putty and the virtual "MSP430 Application UART" com port. The jumpers on J3 are set to HW UART.

 

But I need some help understanding how the HW UART and the UART on P1.1 and P1.2 belong together or don't. I don't know if they are the same or something different. I am confused:

 

What exactly changes when setting the jumpers on J3 to SW UART (virtual com port is still there, but why does my software not work anymore)? Does jumpering to SW UART affect P1.1/P1.2?

 

Can I use the HW UART (like I am doing right now) together/independent from P1.1/P1.2? What is happening with P1.1/P1.2 right now, while using HW UART on virtual com port?

 

I want to connect another IC's UART to P1.1/P1.2 to communicate with my MSP430. Is it important how jumpers @ J3 are set? Can I use HW UART for that? Is it possible to have this communication while still using the virtual com port with HW UART?

 

You see, many questions, but just one basic problem in understanding.

It would be nice if you could sum things up and make it clear to me. :)

 

Thanks a lot!

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Early versions of LP ( <1.5) were designed to be used with chips that didn't have USCI, just USI.

P1.1 was assigned to TXD, P1.2 to RXD. UART was possible in software only.

When MSP430G2553 came along, USCI's RXD was on P1.1, TXD on P1.2.

TI changed J3's RXD/TXD with introduction of LP v1.5 (for compatibility with legacy code.)

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It was discussed on another topic, so check there, and if after reading you still have some questions, ask here.

 

http://forum.43oh.com/topic/3948-ttl-uart-and-ftdi-what-is-what-and-for-what

 

Hi jazz, thanks for the link. After reading the topic, this is what I understood so far

 

- With HW UART I can use either the virtual com port or P1.1/P1.2.

- If I want to use the HW UART on the virtual com port along with another UART communcation to some IC, I have to implement the latter by  software/timers.

 

If jumpers J3 are set to SW UART, I can use the HW UART functionality at P1.1/P1.2? Why is it then called SW UART?

If jumpers J3 are set to HW UART, are P1.1/P1.2 "free" for other purposes?

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Hi jazz, thanks for the link. After reading the topic, this is what I understood so far

 

- With HW UART I can use either the virtual com port or P1.1/P1.2.

- If I want to use the HW UART on the virtual com port along with another UART communcation to some IC, I have to implement the latter by  software/timers.

 

If jumpers J3 are set to SW UART, I can use the HW UART functionality at P1.1/P1.2? Why is it then called SW UART?

If jumpers J3 are set to HW UART, are P1.1/P1.2 "free" for other purposes?

 

Launchpad has USB-UART bridge (virtual COM port) limited to 9600 bps. It can be used for target chip in socket, for external chip, or for any other (not MSP430 related) device where UART (3.3V TTL) is needed. You need to take BRXD/BTXD lines from Launchpad with removed jumpers (from BRXD/BTXD), and GND line from somewhere and connect it to your board. With this setup USB-UART bridge will work with your device, and not Launchpad target chip.

post-26480-0-74207500-1371301938_thumb.gif

 

If you check Launchpad target chip pinout, you can see that P1.1and P1.2 are used also for hardware UART (UCA0RXD, UCA0TXD). So this pins can be used for software/hardware UART (hardware RX pin = software TX pin, hardware TX pin = software RX pin), but not in the same time for some other function. If you want to use this pins (on target chip) for something else, just remove jumpers (from P1.1/P1.2).

 

post-26480-0-83141700-1371302443_thumb.gif

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