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asjad
Joined: 09 Mar 2004
Posts: 52
Location: Greater Manchester - UK
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| ccs instructions |
 Posted: Wed Mar 10, 2004 7:10 am |
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Does anyone know if you can put literal values in registers instead
of calling functions all the time??
e.g
set_tris_d(0x00); //calls a function
trisd(0x00); // literal value, no function called, faster execution
-------------------------------------------------------------------------
I think that you would have to amend the header file.
Any ideas??
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Best Regards |
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Ttelmah
Guest
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| Re: ccs instructions |
| Posted: Wed Mar 10, 2004 7:29 am |
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| asjad wrote: | Does anyone know if you can put literal values in registers instead
of calling functions all the time??
e.g
set_tris_d(0x00); //calls a function
trisd(0x00); // literal value, no function called, faster execution
-------------------------------------------------------------------------
I think that you would have to amend the header file.
Any ideas?? |
Have you looked at the assembler generated?. In fact CCS, does not 'call a function' for most simple operations. So if you execute 'output_b(20)', the assembler generated, is just to load the W register with the value (20), and then to output it to the port (provided you have fast_io selected). The 'set_tris_d' that you quote, will do the same.
You can generate exactly the same code, by using the #byte operation if you really want to, so (of a 18Fxx for instance), you could code as:
#byte TRISD=0xF95
TRISD=0;
The resulting assembler though is exactly the same, and you will gain nothing in speed.
Best Wishes |
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Chas
Guest
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| Except set_tris_c() |
| Posted: Wed Mar 10, 2004 8:44 am |
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Most of the time you can set registers directly, but watch out the the TRISC register. There can be a problem with "read-modify-write" on that register. As suggested by Microchip, CCS maintains a mirror of the TRISC register which they "r-m-w" and then copy the whole register to the TRISC register. Refer to the section in the data sheet on the I/O ports, such as 3.3 in the 877 manual.
I would also recommend using the built in functions to set the OPTION register. There is a specific routine that Microchip recommends following to change the assignment of the WDT/Timer0 prescaler. CCS does this with the setup_counters() and setup_timer_0() functions. I don't have my compiler here so I may have spelled these two functions wrong but you can find them in the help. This problem is detailed in the mid-range micro reference manual from Microchip in section 26. |
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