Lua: Hexadecimal Word to Binary Conversion

Question

I'm attempting to create a Lua program to monitor periodic status pings of a slave device. The slave device sends its status in 16-bit hexadecimal words, which I need to convert to a binary string since each bit pertains to a property of the device. I can receive the input string, and I have a table containing 16 keys for each parameter. But I am having a difficult time understanding how to convert the hexadecimal word into a string of 16-bits so I can monitor it.

Here is a basic function of what I'm starting to work on.

function slave_Status(IP,Port,Name)
    status = path:read(IP,Port)
    sTable = {}
    if status then
        sTable.ready=bit32.rshift(status:byte(1), 0)
        sTable.paused=bit32.rshift(status:byte(1), 1)
        sTable.emergency=bit32.rshift(status:byte(1), 2)
        sTable.started=bit32.rshift(status:byte(1), 3)
        sTable.busy=bit32.rshift(status:byte(1), 4)
        sTable.reserved1=bit32.rshift(status:byte(1), 5)
        sTable.reserved2=bit32.rshift(status:byte(1), 6)
        sTable.reserved3=bit32.rshift(status:byte(1), 7)
        sTable.reserved4=bit32.rshift(status:byte(2), 0)
        sTable.delay1=bit32.rshift(status:byte(2), 1)
        sTable.delay2=bit32.rshift(status:byte(2), 2)
        sTable.armoff=bit32.rshift(status:byte(2), 3)
        sTable.shieldoff=bit32.rshift(status:byte(2), 4)
        sTable.diskerror=bit32.rshift(status:byte(2), 5)
        sTable.conoff=bit32.rshift(status:byte(2), 6)
        sTable.envoff=bit32.rshift(status:byte(2), 7)
    end
end

I hope this approach is understandable? I'd like to receive the Hex strings, for example 0x18C2 and turn that to 0001 1000 1100 0010, shifting the right-most bit to the right and placing that into the proper key. Then later in the function I would monitor if that bit had changed for the better or worse.

If I run a similar function in Terminator in Linux, and print out the pairs I get the following return:

49
24
12
6
3
1
0
0
56
28
14
7
3
1
0
0

This is where I am not understanding how to take each value and set it to bits

I'm pretty new to this so I do not doubt that there is an easier way to do this. If I need to explain further I will try.

Answer 1

tonumber(s, 16) will convert hex representation to decimal and string.char will return a symbol/byte representation of a number. Check this recent SO answer for an example of how they can be used; the solution in the answer may work for you.

Answer 2

I'd approach this in a different fashion than the one suggested by Paul.

First, create a table storing the properties of devices:

local tProperty = {
    "ready",
    "paused",
    "emergency",
    "started",
    "busy",
    "reserved1",
    "reserved2",
    "reserved3",
    "reserved4",
    "delay1",
    "delay2",
    "armoff",
    "shieldoff",
    "diskerror",
    "conoff",
    "envoff",
}

Then, since your device sends the data as 0xYYYY, you can call tonumber directly (if not a string). Use a function to store each bit in a table:

function BitConvert( sInput )
    local tReturn, iNum = {}, tonumber( sInput ) -- optionally pass 16 as second argument to tonumber
    while iNum > 0 do
        table.insert( tReturn, 1, iNum % 2 )
        iNum = math.floor( iNum / 2 )
    end
    for i = #tProperty - #tReturn, 1, -1 do
        table.insert( tReturn, 1, 0 )
    end
    return tReturn
end

And then, map both the tables together:

function Map( tKeys, tValues )
    local tReturn = {}
    for i = 1, #tKeys do
        tReturn[ tKeys[i] ] = tValues[i]
    end
    return tReturn
end

In the end, you would have:

function slave_Status( IP, Port, Name )
    local status = path:read( IP, Port )
    local sTable = Map( tProperty, BitConvert(status) )
end