8-bit Microcontrollers中的主题 how to define a byte data for bit addressable?

how to define a byte data for bit addressable?

eos33 — Tue, 06 Jun 2006 09:13:45 GMT

hi all,

i am the newbie of the Freescale MCU and trying to learn it base on the DEMO9S08QQ8 demo board.

how to define a byte that stores the status(or control) flag and access the bit independently?

like Bit7=LED7,Bit6=LED6...

then

LED7=1

LED6=0....etc..

thank you for your kindly help.

Message Edited by eos33 on 06-05-2006 09:15 PM

Re: how to define a byte data for bit addressable?

rhinoceroshead — Tue, 06 Jun 2006 10:28:41 GMT

Are you working in C or assembly?

Re: how to define a byte data for bit addressable?

bigmac — Tue, 06 Jun 2006 11:34:40 GMT

Hello,

If you were assembly programming, there are instructions to do bit manipulations directly, however I assume you will be working in C where the situation is a little more complex.

Firstly, if you are referencing any of the defined I/O registers for the device, CW has already done the preparation (within the file MC9S08QG8.h), so the following would work -

#define LED6 PTBD_PTBD6
#define LED7 PTBD_PTBD7

LED6 = 1;
LED7 = 0;
if (LED6 == 1) {

}

etc.

If you are creating your own status register in RAM, you will need to do the setup yourself. The following example uses a similar method to the CW header file.

/* LDSTAT - LED Status register */
typedef union {
byte Byte;
struct {
   byte        :1;
   byte        :1;
   byte        :1;
   byte        :1;
   byte        :1;
   byte        :1;
   byte LED6   :1;
   byte LED7   :1;
} Bits;
} LDSTATSTR;

LDSTATSTR _LEDSTAT;
#define LDSTAT  _LDSTAT.Byte
#define LED6    _LDSTAT.Bits.LED6
#define LED7    _LDSTAT.Bits.LED7

Regards,
Mac

Re: how to define a byte data for bit addressable?

eos33 — Wed, 07 Jun 2006 14:26:21 GMT

hi all,

i am working in C.

refer to bigmac's example i have done it and really works fine.

thank you..