SIMM-Sys project

Key concept

SIMM-Sys is a modular system. Some modules are application-independt and thus can be re-used in many project, some are not. There are three kind of modules the SIMM-Sys concept indentifies:

The CPU cards contain the central controller memory and some optional peripherials. These cards are standard components and can be ordered from RCS Ltd. Anyone however is encouraged to develop their own CPU cards using the SIMM-Sys guidlines.
The Peripherial cards contain interface ciruits for the outside world. There is no limitation of the features implemented on those cards but the main focus of RCS developed cards will be on providing some kind of networking capability. These cards are more-or-less standard components and can be ordered from RCS Ltd. From time-to-time however it might be required for an application to modify an existing or design a new peripherial card.
The Mother Boards are the central phisycal elements of the system. They provide mechanical foundation for the product, distribute power to the cards, provide proper peripherial connectors and contain real-world interfaces, like AD/DA converters, optocouplers, etc. Again, there is no limitation what a motherboard should actually perform, this is only the main idea behind the concept. These are custom components and generally should be design for each application. RCS Ltd. provides a line of general-purpose mother-boards that can handle a wide varity of the applications however the key concept is to develop this component specifically for the application.

The number of modules in a system built around with SIMM-Sys is limited. There can be only one CPU card in a system (i.e. no multi-mastering is supported on the SIMM-Sys bus. Multi-processor systems however can be built using specially designed motherboards and/or communication cards). The number of peripherials connected to a CPU card is limited to three. If the motherboard provides perihperial functions the number of SIMM-Sys peripherial modules that can be connected to a CPU card is limited to two.

Physically SIMM-Sys utilizes the the 72-pin SIMM socket used for 36-bit FPM and EDO RAMs in the near past to connect the above mentioned components together. This socket is reliable, small and cheap. Both CPU and peripherial cards use the same socket and pin-out however they are not inter-changeable bacouse of the plug-and-play back-plane wireing. However no demage should happen to the cards if inserted to a wrong socket.

Simm-Sys is build around a simple 16-bit bus system. From the 72 available pinns on the SIMM-Sys socket 37 are used for the busses address, data, select, interrupt, etc. pins. 6 pins are reserved for power lines and the rest are used as I/O pins of the cards. These pins are user-defined and can rovide any functionality. This eliminates plugging things on the small SIMM cards which would reduce reliability. For the user-defined pins there are however some default layouts for various functions. It is recommended to use those layouts if possible.

The whole concept is somewhat the contrary of the usual approach to a modular system. For example in the PC you have a Motherboard holding all common functionality and application- specific extension-cards plugged into it. The problem with this approach is that if the form-factor of the motherboard does not fulfill your needs there isn't much you can do. Also it might contain functionality not required in your application still it's their consuming power and space.

The SIMM-Sys concept works in the opposite way. You have to design a motherboard containing all application-specific circuits and plug-in standard function boards to implement common features. The number of supported cards (for a certain limit) the type of supported cards, the size and layout of the whole system is up to you.

There are two kinds of SIMM-Sys cards planned. CPU-cards and peripherial (I/O) cards. No analog cards are planned. The reason for this this: the analog part is the most application-specific one thus probably will be implemented on the custom-designed motherboard. The analog and digital parts cannot be adequately separated on such small devices. The plus connector between the converter and the analog world further reduces performance. If there are common required analog functionality it is possible to design semi-custom or off-the-self motherboards implementing that particular analog functionality.