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akokyaw
Joined: 11 Feb 2005
Posts: 24
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| I/O port problem |
 Posted: Sat Feb 12, 2005 6:39 am |
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Hi,
Any one can help me? I am a new in CCS C compiler and have a few questions.
1. How to set PORTB as outputs?
2. can i use PORTB = 0xFF as in assembly language.
Thank in advanced,
AKO |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Sat Feb 12, 2005 8:15 am |
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| Quote: | | 1. How to set PORTB as outputs? |
Call output_b(value), this will automatically set PORTB as an output with every call to this function.
If you want to avoid the overhead of setting the I/O-direction register each time you can add: | Code: | #use FAST_IO(B)
SET_TRIS_B( 0x0F );
// B7,B6,B5,B4 are outputs
// B3,B2,B1,B0 are inputs
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at the start of your program.
PORTB needs special care because it is mixed with several other internal devices like the A/D-converter which are sometimes enabled by default, this is different for each PIC model. It's good programming practice to make sure these devices are disabled, so always add setup_adc_ports(NO_ANALOGS) if you are not using the ADC.
Normally the CCS added startup code will configure the A/D-pins as all digital, but sometimes CCS screws up (for example v3.216 for the PIC18F2520 had a bug which configured AN1-AN11 as analog inputs, this was fixed without notice in v3.218).
| Quote: | | 2. can i use PORTB = 0xFF as in assembly language. |
Yes, but you have to define the name of PORTB first. CCS doesn't supply a header file with these names, but for some devices like the PIC18F452 users have posted these include files in this newsgroup.
Method 1, using #byte: | Code: | // Warning: Memory at x is not exclusive to this variable.
// Other variables may be located at the same location.
#byte PORTB = 0xF81
PORTB = 0xFF; // Set port B as all inputs |
Method 2, using #locate: | Code: | // #LOCATE works like #BYTE however in addition it prevents C from using the area.
unsigned char PORTB;
#locate PORTB = 0x0F81
*PORTB = 0xFF; // Set port B as all inputs |
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akokyaw
Joined: 11 Feb 2005
Posts: 24
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| I/O port problem |
| Posted: Tue Feb 15, 2005 9:53 am |
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Thank Ckielstra,
Thank, your info help me a lot.
Rgds,
AKO |
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