convert 16 bit port to Char
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From: Thomas Magma on 3 Jul 2008 14:24 Hello, I'm programming in C on a dsPIC33F and I'm trying to find the most efficient way to save a 8-bit signed value found on the LSByte of PORTD to a CHAR. That is, the lower byte of PORTD contains a signed integer that is 8-bits wide and I need to save it to a CHAR data type. I don't care what is on the upper byte of PORTD. What would be the most efficient way to do this? Thanks. Thomas
From: Roberto Waltman on 3 Jul 2008 15:28 "Thomas Magma" wrote: >... I'm trying to find the most efficient >way to save a 8-bit signed value found on the LSByte of PORTD to a CHAR. >That is, the lower byte of PORTD contains a signed integer that is 8-bits >wide and I need to save it to a CHAR data type. I don't care what is on the >upper byte of PORTD. Just read the value and assign it to a char variable. Assuming you do not need to do anything special to access the port: #define INT16 [put right type here] INT16 * port_d = [put address of PORTD here]; char c; .... c = *port_d; .... -- Roberto Waltman [ Please reply to the group, return address is invalid ]
From: Frank Buss on 3 Jul 2008 15:51 Roberto Waltman wrote: > #define INT16 [put right type here] You should use typedef instead of #define > INT16 * port_d = [put address of PORTD here]; You should add a cast to avoid compiler warnings for C compilers: INT16* port_d = (INT16*) [put address of PORTD here]; In C++ not adding a cast would be an error. -- Frank Buss, fb(a)frank-buss.de http://www.frank-buss.de, http://www.it4-systems.de
From: Thomas Magma on 3 Jul 2008 15:52 >>... I'm trying to find the most efficient >>way to save a 8-bit signed value found on the LSByte of PORTD to a CHAR. >>That is, the lower byte of PORTD contains a signed integer that is 8-bits >>wide and I need to save it to a CHAR data type. I don't care what is on >>the >>upper byte of PORTD. > > Just read the value and assign it to a char variable. Assuming you do > not need to do anything special to access the port: > > #define INT16 [put right type here] > > INT16 * port_d = [put address of PORTD here]; > char c; > > ... > c = *port_d; > ... Thanks Roberto, I guess this would make sense if the data representation of the dsPIC33 using the C30 compiler was stored in little endian format. Do you know if it is for sure? Thomas
From: Frank Buss on 3 Jul 2008 16:13
Thomas Magma wrote: > Thanks Roberto, I guess this would make sense if the data representation of > the dsPIC33 using the C30 compiler was stored in little endian format. Do > you know if it is for sure? This would be a problem, if you access a union or cast the int* to char*, but if you first read the int* and then assign it to an char, endian doesn't matter, the lower 8 bits are used all the time, which is what you asked for. Of course, if you read the 16 bit value from PORTD, endian could be a problem. -- Frank Buss, fb(a)frank-buss.de http://www.frank-buss.de, http://www.it4-systems.de |