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ECB bus history
The German firm Kontron defined what is believed to be the earliest bus using the 96-pin DIN 41612 EuroCard connectors. The bus for their Z80 offering used only the A-row and C-row pins; the B-row was left entirely unused to allow for the use of 64-pin connectors in the 96-pin format.
The earliest known RetroBrew bus definition added B-row pin definitions in anticipation of expansion of the Z80 bus to other processors, notably Intel. To this day, the ECB SBC v2 (Z80) does not use the B-row pins.
One error occurred in defining the first RetroBrew bus: confusion between signals RESET (C-31) and RESOUT (C-26). The error resulted in a bad guess at what Kontron's intentions were with these two signals. SBC v1 (Z80) used RESET as an output from the CPU board to peripheral boards, and did not use the RESOUT signal at all. Peripheral boards were designed with this assumption. When it was pointed out several years ago (I am unsure of the date) that Kontron's intention was for RESET to be an input to the CPU board only, and that the CPU board would then put out a signal, RESOUT, to all of the peripheral boards in the system.
The resolution to the above mistake is that all the newer CPU and Peripheral boards have a reset selection jumper to select which RetroBrew reset convention is to be used. Look for a 3-pin jumper header: shorting pins 1-2 indicates the older, erroneous, reset convention for use with older boards; shorting pins 2-3 indicates the use of the Kontron convention. The Kontron convention is required if RESET is to be input from any of the ECB backplanes, and only newer board may be used in such a system. Old CPU boards have a 2-pin Reset (in) connection as well as a Reset switch right on the CPU card.