The IMSAI SIO 2 Rev-3 is a faithful reproduction of the 1975 SIO USART board.
The SIO 2 is available in a one-port (SIO 2-1) or a two-port (SIO 2-2) configuration.
Each port is a complete synchronous/asynchronous USART (8251A) with TTL, RS-232, and current loop interfaces.
A port expansion kit is available to convert an SIO 2-1 to an SIO 2-2.
When built to the instructions in the new User Manual,
the SIO 2 is electrically and mechanically identical to the 1975 IMSAI SIO 2 Rev-3.
Order one from the list below. The kits are complete with everything you need except solder and tools unless otherwise stated.
They even come with a professionally printed user manual.
Please note that the SIO 2 does not come with the connecting cables to the back frame of the cabinet.
Those are purchased separately from the options. You will need one CABLE A for each SIO port.
Be sure to hover over any 
icons for more information.
Most builders won’t need anything else besides one of the above complete kits.
To skip over the options go to More Information to get links to useful resources.
If you're an advanced builder and want to see all the options, read on.
You may order a bare printed circuit board for you to use your own parts.
Be advised that individual parts are not available to bare board customers unless they are explicitly in the parts list below.
| Description | Part Number | Availability | Unit Price (USD) | Quantity | Ordering |
IC, SN75188, Quadruple Line Drivers, DIP-14 | 39-06075188 | In stock | $4.00 | | |
| IC, SN75189A, Quadruple Line Receivers, DIP-14 | 39-06075189 | In stock | $4.00 | | |
| IC, SN75452, 30-V Dual output driver with NAND logic inputs, DIP-8 | 39-06075452 | 8 in stock, more in 10 days | $4.00 | | |
| IC, 8216 Bi-directional Bus Driver, DIP | 39-15008216 | In stock | $5.00 | | |
| IC, 8251A, Programmable Communications Interface, DIP | 39-15008251 | 6 in stock, more in 10 days | $7.00 | | |
| IC, N8T97N, Hex Tri-state Buffer, DIP | 39-18008970 | In stock | $5.00 | | |
| Optoisolator, Transistor with Base, DIP-6 (Dual In-Line Package) | 45-01015010 | 16 in stock, more in 10 days | $4.00 | | |
All components in the SIO 2 Rev-3 kit are new production with the exception of the 7425, 74177, 8212, 8216, and 8251A ICs which are new old stock.
The content of the user manual is reproduced from an original SIO 2 user manual from San Leandro, plus new content.