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no kit, PCB and individual parts available in the webshop

SwitchTOS V1.0 

The ATARI ST getting fit for a long life, and you will learn how easy it is to switch between multiple operating systems.

SwitchTOS is an adapter for switching between 4 operating systems for ATARI ST with 6 TOS ROMs, e.g. motherboard C070523-001 Rev C. Because the circuit consists of only a few standard parts and hobbyists should have a subset in stock, we do not offer a kit for the time being, but the PCB and individual parts.

The special feature of SwitchTOS is that the switching takes place with the reset button and therefore no switching elements are required on the housing. A permanent setting for a specific TOS is also possible with two jumpers.The 4 new TOS versions are stored in 256kB blocks one after the other in the flash (even if only 192kB are used each) and switched forward by one block with each keystroke, strictly speaking in the order 1-2-3-0 after cold start. A possible assignment would be e.g. TOS1.02 - TOS1.04 - EmuTOS - KaosTOS.

The schematics of SwitchTOS is simple, the difficulty with the 6 ROM motherboards is the limited space under the power supply. Headers cannot be used, SwitchTOS works with angled pins pulled of headers.

SwitchTOS is open source under the GPL license. The schematic will be published on Github. We do not offer a programming service for Flash, you can only buy the unprogrammed 4Mb Flash from us. For programming, for example, the well-known Willem programmer is suitable.

SwitchTOS is primarily intended for use with 192kB TOS versions, further modifications are required for 256kB TOS versions. The GLUE must not trigger a bus error at Exxx addresses, an address comparator (7485/74688) must recognize the Exxx addresses and drive the 256k signal in SwitchTOS, the solder jumpers on SwitchTOS must be reset (connect JP3, disconnect JP4).

TIP: Get to know the project first, then order. In particular, first find a source for the TOS versions, a programming option, then use the parts list to find the parts that are still needed.

RefDes Description Value Footprint Approved parts MPN Webshop ID Qty
  Flash 512k x8 55ns PLCC32 Microchip SST39SF040-55-4C-NHE SST39SF040-55-4C-NHE or    
      PLCC32 Microchip SST39SF040-55-4I-NHE SST39SF040-55-4I-NHE or    
U20, U50 Flash Memory Flash 512k x8 70ns PLCC32 Microchip SST39SF040-70-4C-NHE SST39SF040-70-4C-NHE or 8088 2
      PLCC32 Microchip SST39SF040-70-4I-NHE SST39SF040-70-4I-NHE    
U20, U50 Flash Memory Socket PLCC32 SMT PLCC32 Multicomp MC-32PLCC-SMT MC-32PLCC-SMT or    
      PLCC32 Preci-Dip 540-88-032-17-400 540-88-032-17-400 or other 8099 2
      SO14 NXP 74HC11D 74HC11D    
      SO14 TI CD74HC11E / SN74HC11D CD74HC11E / SN74HC11D    
U1 AND Gates Triple 3-Input AND SO14 NXP 74HCT11D 74HCT11D 7085 1
      SO14 TI CD74HCT11M CD74HCT11M    
U40 Binary Counter 12-Stage Binary Counter SO16 FSC/OnSemi MM74HC4040M MM74HC4040M 7592 1
    for switching by reset button SO16 TI CD74HC4040M CD74HC4040M    
Pins RA for wire connectors and jumpers only for wire connectors and jumpers only 40 pos 0.1” header RA any, for wire connectors and jumpers only Header_2.54mm_male_1x40_RA 7713 1
  Pins RA for Atari sockets U2/U5 for pin extraction only 80 pos double-row 2mm header RA any, for pin extraction only Header_2mm_male_2x40_RA 7714 1
Wire SwitchTOS Wire Set   SwitchTOS Wire Set SwitchTOS Wire Set 8090 1
PCB PCB SwitchTOS (first batch named MultiTOS)     PCB SwitchTOS PCB SwitchTOS V1.0 8089 1



SwitchTOS Assembly Guide