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The MMU board has logic gates that detect this. When the 6809 is in “SYNC mode” waiting for an interrupt, two output pins on the 6809 indicate this condition: BA=1 and BS=0 (called “SYNC Acknowledge” in the datasheet). This instruction blocks until an interrupt occurs (similar to WAI on 65C02).
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To get back to the usual SuperPET memory map, the code executes the 6809’s SYNC instruction. There is no access to the $EFFC latch once in the OS-9 memory map. In this map, the 6809 sees 64K of contiguous RAM from $0000-FFFF, all physically located in the SuperPET expansion RAM. When bit 5 is high, the OS-9 memory map is activated. It expands the SuperPET expansion RAM bank select latch at $EFFC (on the combo board, 74LS273 U36).īit 5 – Unused on Stock / OS9SELECT on MMUīit 6 – Unused on Stock / FIRQDISABLE on MMU The Super-OS/9 MMU is a daughterboard that plugs into the 6809 socket on the SuperPET. For more information on the stock SuperPET, see André Fachat’s pages. The currently selected 4K bank is mapped into $9000-9FFF. Writing to the bank select register at $EFFC selects bank 0-15. The expansion RAM is divided into 16 banks of 4K each. It contains 32K from $0000-7FFF, as a CBM 8032 does, and an additional 64K of expansion RAM. OperationĪ stock SuperPET has a total of 96K RAM. You can also try Super-OS/9 using the VICE emualtor (see below). If you would like to build your own, Jim Brain now sells a PCB and parts kit. I then reverse engineered the board from the photos and built my own working replica using point-to-point soldering. In 2009, I received the Super-OS/9 boot disk and photographs of the original MMU printed circuit board from TPUG members Golan Klinger and Steve Gray. The daughterboard allows a 6809-mode program to select between the normal memory map and one of 64K contiguous RAM ($0000-FFFF) to provide more useful working memory to OS-9. The following commands are supported by different versions of the FLEX operating system.In 1985, Avygdor Moise and other members of the Toronto PET Users Group (TPUG) ported Microware’s OS-9 Level I operating system to the Commodore SuperPET.Īs part of this port, they created a small Memory Management Unit (MMU) daughterboard. Several of the TSC computer languages were ported to UniFLEX.ĭuring the early 1980s, FLEX was offered by Compusense Ltd as an operating system for the 6809-based Dragon 64 home computer. Later, TSC introduced the multitasking, multi-user, Unix-like UniFLEX operating system, which required DMA disk controllers, 8" disk, and so sold in only small numbers. TSC also wrote a version of FLEX, Smoke Signal DOS, for the California hardware manufacturer Smoke Signal Broadcasting this version used forward and back linkage bytes in each sector which increased disk reliability at the expense of compatibility and speed. TSC (and others) provided several programming languages including BASIC in two flavors (standard and extended) and a tokenizing version of extended BASIC called Pre-compiled BASIC, FORTH, C, FORTRAN, and PASCAL. The directory structure was much simplified as a result.
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It was a disk-based operating system, using 256-byte sectors on soft-sectored floppies the disk structure used linkage bytes in each sector to indicate the next sector in a file or free list. While no graphic displays were supported by TSC software, some hardware manufacturers supported elementary graphics and pointing devices.
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All versions were text-based and intended for use on display devices ranging from printing terminals like the Teletype Model 33 ASR to smart terminals.
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It was also later ported to the Motorola 6809 that version was called Flex9. The original version was for 8" floppy disks and the (smaller) version for 5.25" floppies was called mini-Flex.