; macro to mimic the HEX feature of asm6

    .macro hex data

        .local strlen
        .local nib
        .local hiNib
        .local hiNibReady

        ; .strlen will error if user passed us something that is not a string. (good)
        strlen = .strlen( data )
        hiNibReady .set 0

        ; check each character in the string and turn into bytes
        .repeat strlen, I

            nib .set .strat(data, I)
            ; allow space or underscore or $, but ignore them.
            .if .not ( nib = ' ' .or nib = '_' .or nib = '$')

                ; convert nib if in range for 0..9 or A..F or a..f
                .if nib >= 48 .and nib <= 57
                    nib .set nib - 48
                .elseif nib >= 65 .and nib <= 70
                    nib .set  nib - 55
                .elseif nib >= 97 .and nib <= 102
                    nib .set nib - 87
                .else
                    .error "Invalid character in hex byte."
                .endif

                ; create a byte if ready

                .if hiNibReady
                    .byte hiNib | nib
                    hiNibReady .set 0
                .else
                    ; if lone nybble at the end of the string, treat it as a byte
                    .if I + 1 = strlen
                        .warning "Incomplete hex byte at end of data."
                        .byte nib
                    .else
                        hiNib .set nib << 4
                        hiNibReady .set 1
                    .endif
                .endif
            .endif

        .endrepeat

    .endmacro