First thought is that you need a generic Buffer sized to the length you want to send. For example:
Code:
LCD_Buffer VAR BYTE[18]
I use the ARRAYWRITE command for what I think you're asking. Here is a piece of code that fills in blanks to my Buffer and loads them for a UART send:
Code:
Send_Vac:                                       ;Send Current Vacuum Reading to Nextion
    tVac = Vac                                  ;Create a Temporary Variable We Can Modify
    ARRAYWRITE NexBuf, ["vac.val="]             ;Start Nextion Command Sequence, Occupies NexBuf[0] >> [7]
    IF tVac > 100 THEN                          ;If 3 Digits
        b0 = tVac / 100                         ; Get the Xxx Value
        NexBuf[8] = b0 + $30                    ; Convert it to ASCii
        tVac = tVac - (b0 * 100)                ; Subtract the Xxx Value from tVac
        IF tVac < 10 THEN                       ;If xXx = 0
            NexBuf[9] = $30                     ;If tVac < 10, it's Zero (ASCii)
        ENDIF                               ;IF tVac < 10
    ELSE                                        ;tVac < 100
        NexBuf[8] = $30                         ;If tVac < 100, 1st Digit is Zero (ASCii)
    ENDIF                                   ;IF tVac > 100
    IF tVac > 10 THEN                           ;If Now Double Digit
        b0 = tVac / 10                          ;Get the xXx Value
        NexBuf[9] = b0 + $30                    ;Convert it to ASCii
        tVac = tVac - (b0 * 10)                 ;Subtract the xXx Value from tVac
    ELSE                                    ;tVac < 10
        NexBuf[9] = $30                         ;If tVac < 10, it's Zero (ASCii)
    ENDIF                                   ;IF tVac > 10
    NexBuf[10] = tVac + $30                     ;Convert xxX to ASCii & Write to Buffer                
    FOR b0 = 11 TO 13                           ;Generate "End of Message" Sequence: $FF, $FF, $FF
        NexBuf[b0] = $FF                        ;Load it to Buffer
    NEXT b0                                 ;FOR b0 = 11 TO 13
    NexBuf[14] = 0                              ;Tells Us To Turn UART TX INT Off
    RotX = 0                                    ;NexFlags.RotX -- Clear RotX Flag
    GOTO Start_TX                           ;No RETURN Needed, Using GOTO Command