 Unlike the Portable PC, the DG-1 laptop could not take regular PC/XT expansion cards.RS232 serial ports were built-in, but the CMOS (low battery consumption) serial I-O chip available at design time, a CMOS version of the Intel 8251, was register incompatible with the 8250 serial IC standard for the IBM PC.As a result, software written for the PC serial ports would not run correctly.