Writing to high/low variable pairs?

[kevj]

Thanks Bruce!


.... I found the relevant part, but I don't understand it.

I see these code snips...

@Timer1 = TMR1L
Timer1  VAR  WORD EXT

and "re-loading the timer is just as simple as..."

T1CON.0 = 0  ; stop timer
Timer1 = Timer1 + TimerConst
T1CON.0 = 1  ; turn timer back on

and "another example"

@Capture = CCPR1L
Capture   VAR  WORD EXT

In the first example...

@Timer1 = TMR1L
Timer1 VAR WORD EXT

"@" is a straight ASM line, apparently defining "Timer1" to equal TMR1L. Though this says nothing for what TMR1H should be called. The second line Timer1 VAR WORD obviously defines Timer1 as a variable for PBP - and the EXT has something to do with not doing something with it until it compiles - I didn't understand what that post was getting at.


I'm also again seeing in the above post the inter-changing of various forms of hex numbering. I see "1234h" as well as "$1234" and again, I don't understand why you would use the hex in the first place as it's difficult to read - and again my question, is there some way to just write the value you want "12,385" in your code and have PBP turn it into binary or hex as required when compiling? The need to have to "hex" all your integers seems like a complicated additional step and I don't understand what it needs to be done.

Thanks.

[Bruce]

If you don't understand Darrels' EXT explanation, you might want to come back to it at some
point, and re-read it. It can be confusing if you don't get it.

However, what you're trying to do doesn't require you to work in binary. You can just create
a word sized variable, perform whatever math you need to on it, and then load it into Timer1
high & low bytes.

TimerConst VAR WORD

This gives you a 16-bit variable. Now you can do things like TimerConst = 9612. TimerConst
= TimerConst * 5. Now TimerConst = 48060. PBP automatically stores the result for you as
two 8-bit binary values.

Everything is stored as binary since the PIC internal structure is 8-bit registers.

To load TimerConst into Timer1 low & high bytes you use TMR1L = TimerConst.LowByte, and
TMR1H = TimerConst.HighByte.

You can't do something like TMR1H:L=48060 since you're dealing with two 8-bit file registers
for TMR1L and TMR1H. And you're dealing with two 8-bit values for TimerConst.

It takes two separate operations. Load the low byte of TimerConst into TMR1L. Then load
the high byte of TimerConst into TMR1H.