Robert Uiterwyk's Micro Basic

In June of 1976 the Southwest Technical Products Corp. newsletter contained the source code for several programs. Two were by Robert Uiterwyk, a text editor and a 4k BASIC Interpreter (Bill Turner wrote the manual for BASIC). At the time MITS was going to sell BASIC (by Micro Soft) for $200. SWTPC was going to try to give away its software.

Many people were writing "Tiny BASIC" programs in 1976 and 1977. This program started as one but later grew into a full 8K version and a disk version. SWTPC (Dec 76 BYTE) sold the 4K version for $4.95 and the 8K version for $9.95.

A feature of this BASIC was the BCD arithmetic. This gave very accurate results but was rather slow. The MITS 6800 BASIC only had 6 digits of precision and would generate incorrect answers very fast.

In 1977 Robert also wrote the first DOS for the SWTPC MF-68 floppy disk system. It was very simple and most users were happy to see it replaced by Mini-FLEX in 1978. The TSC version of BASIC later replaced Robert Uiterwyk's version.

Robert hand wrote the first version on a legal tablet. Here is an interview with Robert from Oct 2005.

Instructions and Listing (50k PDF)

Source Code (27k TXT)

6800 S1 Load File (8k TXT)

I would like to thank Mark Green and Ed Hepler for reporting the following errors in the OCR conversion of the source code from the June 1976 Newsletter.
Michael Holley - March 2006
Corrected Lines
060C 26 F9 BNE NXTL12
0961 81 1E PRINT4 CMP A #$1E
0BAE E7 00 STA B 0,X

Mark Green also has these suggestions to correct program errors.

Hex Address Code Error/Comment
02F7 DEX Should be 2 x DEX
030D DEX Same as above
0541,0542 2 x DEX Needs to be 3 x DEX
061C DES Remove since it leaves Stack pointing one too low.
06F4 LDX BASPNT Needs DEX after - else X is pointing 1 byte too high

This version requires MIKBUG and a MP-C interface card. Additional versions of SWTPC BASIC can be found on the FLEX User Group software page.

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This page was last edited August 14, 2013