The Tandy 1000-TX, introduced during the summer of 1987, includes an on-board
COM port that can be configured as COM1 or COM2.

Unlike the previous COM ports from Tandy, the on-board COM port uses a DB-9
connector arrangement, similar to that used on the IBM-PC(AT) and many other
computers.

Here is the pinouts, with comparable pins on a DB-25 connector

DB-9     Signal    I/O      Description       DB-25
pin                                            pin
---------------------------------------------------
 1        DCD       I       Data Carrier Detect  8
 2        RD        I       Received Data        3
 3        SD        O       Transmit Data        2
 4        DTR       O       Data Terminal Ready  20
 5        GND               Ground               1+7
 6        DSR       I       Data Set Ready       6
 7        RTS       O       Request to Send      4
 8        CTS       I       Clear to Send        5
 9        RI        I       Ring Indicator       22



              9  8  7  6
              o  o  o  o
             o  o  o  o  o
             5  4  3  2  1