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CCP1 F452 Module Inquiry

 
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chingB



Joined: 29 Dec 2003
Posts: 81

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CCP1 F452 Module Inquiry
PostPosted: Sat Feb 05, 2005 3:02 am     Reply with quote

Hello,

I found out that in the F452.H header file particularly the line stated below:
long CCP_1;
#byte CCP_1 = 0xfbe
#byte CCP_1_LOW= 0xfbe
#byte CCP_1_HIGH= 0xfbf

Why is that CCP_1 was declared as a 16bit variable? I try to look at the F452 data sheet and found-out that 0xFBE register address for CCP_1 is an 8bit register?

One more thing CCP_1_LOW has the same address with CCP_1 which is of different data types. I understand that CCP_1_LOW is an 8bit register.

With this the declaration long CCP_1 only uses the lower 8bit rather than the 16bit lval.

Is their another way of defining and using the CCP_1 such that it can be easily ported to other C Compiler?

Anyone can explain it why this is so?

Thnx
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sat Feb 05, 2005 3:25 am     Reply with quote

Read section 14.3 Capture Mode of the 18F452 data sheet.
Read the first sentence in that section.
Mark



Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA

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PostPosted: Sat Feb 05, 2005 1:43 pm     Reply with quote

The CCP register is composed of 2 bytes. A low byte and a high byte. The 16 bit variable is so you can assign the by a 16 value rather than a having to do 2 8bit assignments. It is correct BTW.
chingB



Joined: 29 Dec 2003
Posts: 81

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PostPosted: Sun Feb 06, 2005 1:00 am     Reply with quote

I want to change the definition of the line stated below <w/o using #byte>:
Code:

long CCP_1;
#byte CCP_1 = 0xfbe
#byte CCP_1_LOW= 0xfbe
#byte CCP_1_HIGH= 0xfbf


with code below

Code:

#define CCPR1L    (0xFBE)
#define CCPR1H    (0xFBF)

long iCCP_1;
#define iCCP_1            *((unsigned int *) CCPR1L)
#define iCCP_1_LOW    *((unsigned int *) CCPR1L)
#define iCCP_1_HIGH   *((unsigned int *) CCPR1H)


Would this code replacement possible? I need your comments and suggestions such that my code will not use the #byte preprocessor for easy porting to other PIC C-Compiler.

Thanx
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