In SX Microcontrollers, SX/B Compiler and SX-Key Tool, andbell wrote:

Hello Everyone,

 

Currently, I am designing a board which will be using 11-12 SX-48BDs (I need a ton of I/O). I do not need to synchronize the SXs if I use interrupts, but synchronizing them could save memory and clock cycles.  I have a few questions regarding oscillator considerations:

 

When using a TTL oscillator I noticed it only needs to be connected to the OSC-1 pin, but crystals get connected to OSC-1 and OSC-2.  OSC-2 is listed as an output. Does it buffer the clock signal, and if so would it be possible to daisy chain many SXs' together in this fashion (allowing for propogation delay)?  Other possibilities I was looking at included using a clock distribution IC, but most are for LVDS or CMOS signals, not TTL.

 

My other concern is that the SX-48BD is a SMD, and I am going to need to add a header for in circuit programmability.  I have seen designs using a jumper to disconnect the oscillator during programming, but I am worried about passing a 50MHz clock signal through a jumper, particularly if it is from a crystal oscillator.  Could stray capacitances and contact resistance cause poor oscillation/stability?  Solutions I have been looking at include using an analog mux with a hi-Z state during programming or using a relay to open the crystal.  

 

I know that this is a lot to ask, and I would appreciate any input/suggestions.

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