It's quite easy to implement a byte-wide parallel interface between the two microcomputers, using 8 data pins and data available/ready lines to handshake byte movement across the interface. Meanwhile, I've returned to my dual Arduino solution, this time using the second Arduino merely as a display processor. I'm getting some assistance on the Arduino forum but so far there is no obvious solution in sight. Anecdotally, the Ethernet card is said to not play nicely and opinion seems to be that most devices tend to behave as if they are the only user of the SPI.

It's not clear to me yet whether this is the display itself that is at fault or if it is the victim of one of the other users misbehaviour. The Ethernet card and SD RAM play nicely together but the display Flash ROM breaks the SPI interface. The Flash ROM which holds the fonts on the display card.I have three devices that need to access the SPI. Each device is supposed to request service by asserting a hardware select line. Immediately I ran into a quite unexpected problem! The Arduino has a high speed Serial Peripheral Interface (SPI), which permits cooperating devices to share a bidirectional port. I made a start on integrating the display, multiplexer and encoder software into a single executable running on one processor.

I've been quite busy with other things recently so there hasn't been significant progress for a few days but I do have a few notes of potential interest to share.

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