Access single bit in a word variable

[jackjames]

A question:
Is it possible to access a single bit of a word variable in this way?
Dim Wa as word
dim Bi as byte
Bi = 15
Wa.Bi = 1
and also:
Result = Wa.Bi

---

Resolved: Use variable.bit addressing. Compiler builds after 6/6/2021 now checks the source variable type is a bit or a constant.

[Anobium]

Yes.

and, you can set set a bit within a variable, use this method:

Dim my_variable as byte
Dim my_bit_address_variable as byte

my_variable = 0
my_bit_address_variable = 7

'Sets bit 7 of my_variable therefore 128
 'Where 1 or 0 or any bit address is valid
my_variable.my_bit_address_variable = 1  

[jackjames]

Thanks

[jackjames]

I wrote two routines and did some tests with Simul Ide.
They don't seem to work well, both SetBit and GetBit.
I create a word variable, assign 0, set bit 0 to 1 and then go to read it. I should be reading 1 and reading 0 instead.

Sub SetBit (BitArray As Word, In BitNum As Byte, In BitState As Byte)
        bitarray.bitnum=bitstate
End Sub

Function GetBit (In BitArray As Word, In BitNum As Byte) As Byte
        getbit = bitarray.bitnum
End Function

[Anobium]

This is a very odd approach. The sub and function will be slow, even if it worked.

Just use variable_name.bit_name = 1|0 and targetBitVar = variable_name.bit_name

Do these work? If these do not work then the sub and function will fail.

[stan cartwright]

Hi @jackjames. your code is above my capabilities.
I would if testing a bit .... AND the var with zero except the bit which would be set.

[jackjames]

Yes, if the word variable is = 0 and I raise bit 0 the value I have to read is 1, obviously if I also raise bit 2 I have to read 3 and so on with all 16 bits.
Unfortunately, in the simulation with Simul Ide i the read values ​​are not exact.

[Chris Roper]

Have you tried PICSimLab?

https://sourceforge.net/projects/picsim/
lcgamboa is very quick to replay and make changes if we find any bugs and it has a Small but representative selection of devices including Devices with PPS and an Arduino UNO simulation.

I tend to use SimulIDE if I am testing a potential hardware interface but PICSimLab is my go to for testing Libraries and functions.

[stan cartwright]

Er nor really @jackjames, I am not into clever basic. I thought var and 0x00000001 would test bit 0 as would var and 0x00000010 test bit 2 etc.
Or you could test any bits at the same time var and 0x11001010
Am I missing something here cos I test bits in bytes sometimes. What's different about word vars?

[jackjames]

@stan:
You now gave me the example using an 8-bit variable.
In this case, accessing the single bit of a byte-type variable works.
The problem arises when you have to read / write the bits in a 16-bit word type variable.

[stan cartwright]

@jackjames. I'm thinking there's no way to and a word with another word so get your point but why can't the hi/lo bytes be masked with and? There is a method of using the hi or lo byte of a
word var.
Code that directly addresses bits of a var are probably masking bytes anyway and are probably
slower.
In your original post you say access the bits in a word and thought you just meant read them.
To set the bits I guess you or the mask.

[Anobium]

My question in my post above https://sourceforge.net/p/gcbasic/discussion/579126/thread/cb0f83126a/#61fb/065d/c332

Does the basic functionality work when not in a sub/function? This is a new capability and may not work as expected.

[stan cartwright]

Function GetBit (In BitArray As Word, In BitNum As Byte) As Byte
getbit = bitarray.bitnum
End Function

I thought bitnum would only be 0 to 7.

[jackjames]

I solved the problem and now both the sub and the two functions work.
Practically the compiler does not like the variable with the status of the bit (1/0) in byte format.
Passing it as BIT, both the Sub and the Functions work perfectly.
Here is the written listing to perform the tests and the output result.
Tested with SimulIde.

Source:

        Dim ww1 As Word
        Dim b1 As Byte
        Dim c1 As Byte
'       -
'       -
        ww1=0
        b1=8
        c1=1
        Dim d1 As Bit
'       -
        HSerPrint "ww1:"
        HSerPrint ww1
        HSerSend 13
        HSerSend 10
'       -
        ww1.15=1
        HSerPrint "ww1 Direct Bit access:"
        HSerPrint ww1
        HSerSend 13
        HSerSend 10
'       -
        ww1.1=1
        HSerPrint "ww1 Direct Bit access:"
        HSerPrint ww1
        HSerSend 13
        HSerSend 10
'       -
        ww1=0
        b1=8
        ww1.b1=1
        HSerPrint "ww1 Bit access:"
        HSerPrint ww1
        HSerSend 13
        HSerSend 10
'       -
        ww1=0
        b1=15
        d1=1
        ww1.b1=d1
        HSerPrint "ww1 Bit access:"
        HSerPrint ww1
        HSerSend 13
        HSerSend 10
'       -
        ww1=0
        SetBit ww1, b1, d1
        HSerPrint "ww1 Sub SetBit:"
        HSerPrint ww1
        HSerSend 13
        HSerSend 10
'       -
        b1=15
        HSerPrint "GetBit:"
        HSerPrint GetBit(ww1, b1)
        HSerSend 13
        HSerSend 10
'       -
        HSerPrint "Getbit2:"
        HSerPrint GetBit2(ww1, b1)
        HSerSend 13
        HSerSend 10
'       -
'       -
'       ========================================================================
'       Setta alto o basso un determinato bit di una variabile.
'       ------------------------------------------------------------------------
Sub SetBit (BitArray As Word, In BitNum As Byte, In BitState As Bit)
        bitarray.bitnum=bitstate
End Sub
'       -
'       -
'       ========================================================================
'       Legge un determinato bit da una variabile
'       ------------------------------------------------------------------------
Function GetBit(In BitArray As Word, BitNum As Byte) As Bit
        Repeat BitNum + 1
           Rotate BitArray Right
        End Repeat
        GetBit = STATUS.C
End Function
'       -
'       -
Function GetBit2 (In BitArray As Word, In BitNum As Byte) As Bit
        getbit2 = bitarray.bitnum
End Function

This is the result:
ww1:0
ww1 Direct Bit access:32768
ww1 Direct Bit access:32770
ww1 Bit access:256
ww1 Bit access:32768
ww1 Sub SetBit:32768
GetBit:1
Getbit2:1

[Anobium]

What version of the compiler are you using ? var.bit = 0|1 only works on 0.98.07 or greater.

[Anobium]

I think I have identified the issue. See the code below but essential you need to help the compiler to determine which bit of the byte you passed needs to be used.

I have adapted the code. There is an overloaded SUB to show how to resolve to ensure the correct code is generated. Does this work for you?

We should update the help?

Evan

;Program compiled by Great Cow BASIC (0.98.07 2021-05-27 (Windows 64 bit)) for Microchip MPASM
    #OPTION Explicit
    'USART settings for USART1
    #define USART_BAUD_RATE 9600
    #define USART_TX_BLOCKING
    #define USART_DELAY OFF

   Dim ww1 As Word
        Dim b1 As Byte
        Dim c1 As Byte
'       -
'       -
        ww1=0
        b1=8
        c1=1
        Dim d1 As Bit
        Dim d2 as Byte
'       -

        HSerPrintCRLF 2

        HSerPrint "1. Reset ww1 should read 0 :"
        HSerPrint ww1
        HSerSend 13
        HSerSend 10
'       -
        ww1.15=1
        HSerPrint "2. ww1 Direct Bit access should read 32768 :"
        HSerPrint ww1
        HSerSend 13
        HSerSend 10
'       -
        ww1.1=1
        HSerPrint "3. ww1 Direct Bit access should read 32770 :"
        HSerPrint ww1
        HSerSend 13
        HSerSend 10
'       -
        ww1=0
        b1=8
        ww1.b1=1
        HSerPrint "4. ww1 Bit access should read 256:"
        HSerPrint ww1
        HSerSend 13
        HSerSend 10
'       -
        ww1=0
        b1=15
        d1=1
        ww1.b1=d1
        HSerPrint "5. ww1 Bit access  should read 32768 :"
        HSerPrint ww1
        HSerSend 13
        HSerSend 10

        ww1=0xFFFF
        b1=15
        d1=0
        ww1.b1=d1
        HSerPrint "6. ww1 Bit access  should read 32767 :"
        HSerPrint ww1
        HSerSend 13
        HSerSend 10

'       -
        ww1=0
        b1=15
        d1=1
        SetBit ww1, b1, d1
        HSerPrint "7. ww1 Sub SetBit using BIT should read 32768:"
        HSerPrint ww1
        HSerSend 13
        HSerSend 10

        ww1=0
        b1=15
        d2=1
        SetBit ww1, b1, d2
        HSerPrint "8. ww1 Sub SetBit using BYTE should read 32768:"
        HSerPrint ww1
        HSerSend 13
        HSerSend 10


'       -
        ww1=0
        b1=15
        HSerPrint "9. GetBit should read 0:"
        HSerPrint GetBit(ww1, b1)
        HSerSend 13
        HSerSend 10
'       -
        ww1=0
        b1=15
        HSerPrint "A. Getbit2  should read 0:"
        HSerPrint GetBit2(ww1, b1)
        HSerSend 13
        HSerSend 10

Wait 100 ms
'       -
'       -
'       ========================================================================
'       Setta alto o basso un determinato bit di una variabile.
'       ------------------------------------------------------------------------
Sub SetBit (BitArray As Word, In BitNum As Byte, In BtyeState As Byte)
        'Ensure the compiler uses bit 0 of the Byte
        bitarray.bitnum=BtyeState.0
End Sub

Sub SetBit (BitArray As Word, In BitNum As Byte, In BitState As Bit)
        bitarray.bitnum=bitstate
End Sub


'       -
'       -
'       ========================================================================
'       Legge un determinato bit da una variabile
'       ------------------------------------------------------------------------
Function GetBit(In BitArray As Word, BitNum As Byte) As Bit
        'Use C not status.C for portability
        Set C Off
        Repeat BitNum + 1
           Rotate BitArray Right
        End Repeat
        GetBit = C
End Function
'       -
'       -
Function GetBit2 (In BitArray As Word, In BitNum As Byte) As Bit
        getbit2 = bitarray.bitnum
End Function

[Anobium]

@JackJames

See https://sourceforge.net/projects/gcbasic/files/Release%20Candidates/Patches/GCB%40Syn/GreatCowBASIC/

I do think now think this is bug not a usability issue. The compiler was not generating the code ASM when you used a BYTE. So, I have updated the compiler and message file to improved IndirectBitSet handling - the compiler now verifies the source is either a BIT or a CONSTANT.

[jackjames]

I'll do some tests then I'll let you know.

[jackjames]

This is the result of the compilation:

Summary:
Read by GCBASIC:
Input lines: 152
Subroutines: 424
Chip resource usage:
Program Memory: 1699/8192 words (20,74%)
RAM: 74/368 bytes (20,11%)

Assembling program ...
Building symbol table ...
Generating machine code ...
(Assembly time: 0.093 seconds)

Errors have been found:

Error: GCASM: Symbol SYSBITVAR2 has not been defined at BTFSC SYSBITVAR2,5
Error: GCASM: Symbol SYSBITVAR2 has not been defined at BTFSC SYSBITVAR2,6

The message has been logged to the file Errors.txt.

(Total time: 1.261 seconds)

[Anobium]

I need the source code. I cannot reproduce.

Evan

[jackjames]

The source is the program you published:
https://sourceforge.net/p/gcbasic/discussion/579126/thread/cb0f83126a/#bed0

[Anobium]

That has no chip, no pps etc.

Did you add this? if yes. Please attached this source.

[jackjames]

Everything good.
It was my mistake. There were unwanted lines left at the bottom of the file.

[Anobium]

Does the change help? or, did I break something?

[jackjames]

They have been helpful to me.
It seems that everything works, I work on it a bit and see what happens.
Thanks