If by "closet relative popular programing language" you mean "modern programming language" or a programming language that if you knew you could get hired as a programmer, then you are out of luck.
TBASIC is close to early integer BASIC that shipped with the the Apple II, TRS-80, the Commodore and the 4k Basic written by Bill Gates to run on 8080 based home built computers.
It is hard to find much documentation. This is a link to the Commodore BASIC:
http://www.commodore.ca/manuals/pdfs/Commodore_Basic_4_Users_Reference%20Manual.pdfUnfortunately there are big differences between these early integer BASIC languages and TBASIC. The biggest differences that I see are:
- TBASIC does not have an "immediate mode". If you type in a TBASIC statement without a line number, it is not immediately executed. To test things you must compile the TBASIC program and either run it under the simulator or download the complied version to actual PLC hardware.
- TBASIC only requires line numbers as a target of a GOTO. This behavior is closer to QBASIC that shipped with PCs running MSDOS.
- TBASIC operates with 32 bit integers. The Commodore, Apple II, and 4K BASICs used 16 bit integers. The QBASIC supported floating point arithmetic as well as integer arithmetic.
- TBASIC has many odd quirks in behavior and like the ancient BASIC dialects is poorly documented.
- TBASIC has a very small subroutine stack depth, so concepts like recursive programming is a very bad idea.
Good luck,
Gary d