Yes, it is possible using TDL to open a Cash Drawer while saving POS Invoice.
Default Collection used while printing POS Invoice can be altered to add a new Object and this Object must contain the same method names as declared in other POS Objects with the required Escape Sequences to open the Cash Drawer.
For example :
[#Collection: POSPrinters]
Add : Object : After : Epson TM T88III Compatible : TVS T88III Compatible
;; Escape commands compatible with all Epson POS printers.
[Object: TVS T88III Compatible] ;; Thermal Printer
Name : $$LocaleString:"TVS T88III Compatible"
;; Initialization strings
POSInit : "0x1b 0x40" ;; ESC "@" - Init printer
;; Attributes
POSPrintFont : "0x1b 0x21 0x01" ;; ESC "!" 1 - Condensed font (Font B) selected as printing font
POSPrintFontCPI : 10 ;; Character per inch for Condensed font
POSPrintFontLPI : 6 ;; Lines per inch for Condensed Font
;; Carriage Movement
POSLineFeed : "0x0a" ;; LF (Line Feed)
;; Auto Cutter / Page Eject
POSFeedAndCut : "0x1b 0x1b 0x70 0x30 0x48 0x48"
;; End of code
