Byte variables assigned to Bit variables

[Chuck Curtis]

What determines the value of a bit variable when it is given the value of a byte variable, such as when porta.0=<byte variable>. How is the value of porta.0 determined?

[richard]

portd.0 CAN only be 0 or 1

the compiled asm code will look like this the value of varxxx bit 0 is all that is is considered
if (((_varxxx) & 007fh) <= 0bh)
CHK?RP _PORTD
btfsc _keys, 0
bsf _PORTD, 000h
btfss _keys, 0
bcf _PORTD, 000h
else
CHK?RP _keys
rrf _keys, W
CHK?RP _PORTD
btfsc STATUS, C
bsf _PORTD, 000h
btfss STATUS, C
bcf _PORTD, 000h
endif

[Chuck Curtis]

Without objection, I take that to mean, simply, that the bit variable takes on the value of the LSB of the byte variable.

[richard]

not sure exactly what you are saying

a bit var WOULD be LED0 var BIT
a byte var leds var byte
porta.0 is not a var as such but bit 0 of sfr porta

so for a proper bit var or bit0 of a register

leds = 1

led0 = leds would set led0 to 1

porta.0 = leds would set porta.0 to 1

porta.0 = led0 would set porta.0 to 1


leds =3

porta.0 = leds would set porta.0 to 1


leds = 2

porta.0 = leds would set porta.0 to 0

[mpgmike]

I guess a good place to start in answering your question is with a question; define "Value of...". When we consider the number systems used in software, there is binary where all digits are either 1 or 0; the decimal system where individual digits can be any number between 0 and 9; and the hexadecimal system which has a decimal range of 0 to 15, using characters 0 to F.

Individual pins of the PIC processor belong to a PORT, be it PORTA, PORTC, etc. Any decimal number ranging from 0 to 255 or hexadecimal range of $00 to $FF can reflect each pin of a PORT, but only visually understandable when converted to binary; %0000 0000 to $1111 1111. PORTx = %xxxx xxxx means that each bit in the binary reflects the state of a PORT pin. From there, you can convert the binary (%xxxxxxxx) to hex ($xx) or decimal (xxx).

If this doesn't make sense, search the internet for tutorials explaining the differences of our familiar decimal system and hexadecimal and binary.

[Chuck Curtis]

I frankly don't know how to ask my question any more clearly than I did. Perhaps an example would be better.

Take for example: PORTA.0=128 (or any other decimal number that is within the bounds of one 8 bit byte: 0 to 255). What will the result of PORTA.0 be? One or zero?

[richard]

I frankly don't know how to ask my question any more clearly than I did. Perhaps an example would be better.

incorrect reference to a bit var in the original question did not help either

Perhaps if you explain what and why you are attempting


PORTA.0=128 makes little sense

if you mean to set the pin in a Boolean logic sense where low = zero and high is any value not = zero then perform the operation logically

PORTA.0 = PORTA.0 || 128 <==> PORTA.0=1
PORTA.0 = PORTA.0 || byte-var <==> PORTA.0= !! byte-var

otherwise it will be performed bitwise using bit0

PORTA.0=128 <==> PORTA.0=0