The (more or less) correct syntax would be something like:

Timer1 = OFF;
Shadow16bitT1 = TMR1L + TMR1H*256;
Timer1 = ON;
CCPR1 += Shadow16bitT1;

First of all you must switch off timer 1 so you have no byte-rollover
within the timer while you read.  This period of time should be made
as short as possible, so just copy the timer to a shadow register.
Add it all up in the end.
If you do this instead:

Timer1 = OFF;
CCPR1 += TMR1L + TMR1H*256;
Timer1 = ON;

...the timer will be switched off longer because then you have an
extra 16bit addition to perform.

If you choose not to switch timer 1 off, you _will_ get occational
errors with this method.

If you can't switch timer 1 off, you have to test the values you read
from the timer to make sure you had no rollover.  Something like this:

do {
   L = TMR1L;
   H = TMR1H;
} while (TMR1L < L);   // if this is true, lo-byte rolled over,
                       // and the concatenated value will be wrong
                       // if it rolled over before TMR1H were copied.

With all this in mind, it's not just to make timer 1 a 16bit variable.
The code looks better with it, but works better without it.

-DS


Tuesday, November 09, 1999, 5:00:23 PM, you wrote:

EB> Your syntax is correct.

EB> To make TIMER1 you could use:
EB> unsigned long (uns16, etc) TIMER1;
EB> TIMER1 = TIME1L + TIME1H * 256;

EB> Regards,

EB> Brusque

EB> ----- Original Message -----
EB> From: Roberto Fonseca Iannini <roberto1@LINKEXPRESS.COM.BR>
EB> To: <PICLIST@MITVMA.MIT.EDU>
EB> Sent: Tuesday, November 09, 1999 12:44 PM
EB> Subject: 8 + 8bits variable


>> What's the c syntax to perform an 16-bit sum like:
>> CCPR1 = CCPR1 + TIMER1;
>> Note that TIMER1 wasn't defined by the 1687x.inc. Instead it was made as
>> TIMER1H and TIME1L (each one 8 bits type). The same is true to CCPR1.
>> Summarizing: How can I define or use  a new 16 bit variable called
>> TIMER1 that is formed by TIMERH and TIMERL (MSB and LSB)?
>> (this code is for 16F877)
>> See you guys,
>>
>> Beto.
>>

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