Hi Folks,

I folks I'm the knucklehead that needed help with Timer_A and
reading/decoding and IR signal. I think I (sort of) know what I want
to do but I can't figure out how to set up the TACCTL0 register. I'm
using the free IAR compiler (I've never been all that comfortable with
assemblers).

I want to be able to capture the timer value when a pulse comes in.
My signal is connected to P1.1 which I've set up as an input and set
up CCI0A.

What exactly is the SCCI bit? When do you use it? I'm assuming that
since I'm not outputting anything I don't have to worry about the
OUTMOD0 bits. I'll need to enable the Capture/compare interrupt
enable bit (CCIE) since I plan on using the interrupt.

What does the CCI bit do? The User's guide defines it as:
"Capture/compare input. The selected input signal can be read by this
bit". Are they saying that the Capture/compare input select source
(I've used CCI0A as my IR signal input) will toggle this bit as it
goes high and low? If this is the case is this bit latched at the
time the interrupt occurred?

Does anybody know of any examples of using the Timer_A in capture
mode? I've looked at the TI SLAA134 (Decode TV IR Signals) but the
code is only in assembly I know only real men and women use
assemblers and only wimps use C so call me a wimp.

Thanks again,

Richard Cooke
Lake Forest, CA Start a New Thread

I assume that you are using F2001 and you have a 32768Hz crystal.

See my comments start with *** below.

--- In m..., "Richard Cooke" wrote:
>
> Hi Folks,
>
> I folks I'm the knucklehead that needed help with Timer_A and
> reading/decoding and IR signal. I think I (sort of) know what I
want
> to do but I can't figure out how to set up the TACCTL0 register.
I'm
> using the free IAR compiler (I've never been all that comfortable
with
> assemblers).
>
> I want to be able to capture the timer value when a pulse comes in.
> My signal is connected to P1.1 which I've set up as an input and set
> up CCI0A.

*** In order to do that, you need:
P1DIR:BIT2=0 (it is already 0 after reset)
P1SEL:BIT2=1 (*** your code need to do this)
CAPD:BIT2=0 (it is already 0 after reset)
TACCTL0:CCIS1&0 (it is already 00 after reset)

> What exactly is the SCCI bit? When do you use it?

*** In Compare Mode, when TAR equals TACCRx, the selected input is
latched at this bit and can be read later. This is useful to "sample"
the input at a given time (when TAR==TACCRx).

> I'm assuming that
> since I'm not outputting anything I don't have to worry about the
> OUTMOD0 bits. I'll need to enable the Capture/compare interrupt
> enable bit (CCIE) since I plan on using the interrupt.

*** You are correct. But you need to do more than enable CCIE.
After reset, LFXT1 is enabled and ACLK=LFXT1/12768Hz.
After reset, DCO is running at ~1MHz and MCLK=SMCLK/1=~1MHz.
You need to set TACTL=TASSEL0+MC1 so that TA uses ACLK continously.
You also need to set TACCTL0:CM1&0 to either 01 or 10.
And the rest of TACCTL0 |= SCS+CAP+CCIE.
You need an interrupt service routine.
And you need to set GIE in the SR.

> What does the CCI bit do? The User's guide defines it as:
> "Capture/compare input. The selected input signal can be read
> by this bit".

*** That is correct.

> Are they saying that the Capture/compare input select source
> (I've used CCI0A as my IR signal input) will toggle this bit as it
> goes high and low?

*** Yes. When the input is high, it reads 1.
When the input is low, it reads 0.
As long as P1SEL:BIT2=1, you read this bit instead of P1IN:BIT2.

> If this is the case is this bit latched at the
> time the interrupt occurred?

*** No. I do not think you are not wrong ;)

> Does anybody know of any examples of using the Timer_A in capture
> mode? I've looked at the TI SLAA134 (Decode TV IR Signals) but the
> code is only in assembly I know only real men and women use
> assemblers and only wimps use C so call me a wimp.

*** The IAR MSP430 compiler complains about:
int a = P1IN + P1IN;
But does not complain about:
int b = P1IN + P2IN;
Why?

> Thanks again,
>
> Richard Cooke
> Lake Forest, CA
> Start a New Thread