Starting with the design of low to middle end 16-bit embedded applications including ISA compatible circuitry, a reliable and thoroughly documented bus standard became desirable. While only PC/104 offered an acceptable solution, this ISA bus variation has not evolved over the years, its documentation relies on publications out-of-print and it is treated as legacy bus by its maintainers only. That encouraged us to define an own embedded bus that preserves the well known ISA architecture and the stackable nature of PC/104 while generally clarifying the bus implementation and conservatively incorporating new and useful features. This resulted in the definition of the Extended Stackable ISA (ESISA) embedded bus and architecture.

ESISA defines boards of a compact 4 x 4'' (10.16 x 10.16 mm) form factor with two (optionally three) DIN 41612 connectors. The boards are stackable for eliminating the need of a backplane. The connector standard includes well-defined cabling options paving the way for reliable stack-to-stack or stack-to-system connections. New ESISA modules can be made without or only minor changes to existing ISA designs. Besides, ESISA introduces many new and easy to implement features that ease the task of embedded application hardware design.

Ultimtately, the ESISA standard is completely and thoroughly documented and maintanited in the sphere of a very long term technology development and refinement process that is, the bus specification is kept unchanged instead of extended as new bus standards become available. This continuity is a prime advantage for embedded applications and enables the ESISA bus to become a modern, reliable embedded bus and real alternative to PC/104.