2.1
The International (3U high) size of card with its standard direct gold-plated 0.1" edge connector, is growing in popularity and there are a number of independent suppliers now actively engaged in designing new boards.2.2
There are benefits which apply to suppliers and users alike, if a suitable bus standard can be defined, and for this reason Greenbank Electronics is actively promoting the ISBUS Standard.2.3
The ISBUS standard is still under discussion, but when complete it will define a total of 84 connections – 42 on the 'A' side, and 42 on the 'B' side of the board.2.4
The more important signals of ISBUS are to be found on the ’A' side, and it is a major feature of ISBUS that a worth-while economic system can be built using only these lines, with the 'B' side being held in reserve only for those applications which require the highest performance regardless of cost. ( The 'B' side is used to allow 16-bit microprocessors, extended address space past 64K, and multiprocessors on the same bus etc.2.5
The MZB-3 board has only 'A' side connectors, but these are largely ISBUS compatible. The circuit diagrams and drawings here have been written to help the user conform as closely as practical to the ISBUS standard.
2.6 Some small differences however will still remain, summarised as follows:–
Pin no. Name MZB-3 ISBUS A21 NRST TTL Buffered Open
CollectorA30 NENIN Unused Used A31 NENOUT Unused Used A32 NRFSH Unbuffered Buffered A34 NWAIT Unbuffered Buffered