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SPI Emulation on the MC68HC908JL16 - Tough, at Least for Me :-(

Question asked by Joe Burch on Apr 4, 2010
Latest reply on Apr 9, 2010 by Joe Burch

Hello folks.


I have an application on which I would like to ask your help.  I had been using the SPI interface on a 'legacy' OTP HC05 processor to communicate (one way outgoing, only) to a serial input Phase Lock Loop synthesizer controller - specifically, the MC-154159 chip.  With the HC05, it worked like a charm, every time, day in and day out. It just worked and worked.  Unfortunately, these chips are no longer available......... and smaller is newer and better..............


Recently, I decided to recussitate this project with a new flash based chip in a DIP mountings. I don't think that namy of my hobbyist clients would be interested in a surface mount device and I'm loathe to work on them..  So, I decided to use the MC68HC908JL16 (28 pin) DIP.  By some judicious reuse of some of the pins for several functions, I have it working (almost).


I'm trying to emulate the operation of the SPI using 3 output ports.  I thought it would be relatively easy, but I was wrong.  I hate to tell you how much time I've spent on it.  I have a nice dual input scope and have tried to 'software engineer' the timing on the clock and data ports to get the necessary concurrence for data entru into the PLL (on the rising edge of the 'clock' pulse).  I can't get it to work so far.


Has anyone out there tried to do something similar??


I checked over the Freescale chips to see if there was a DIP device with at least 23 I/O Ports (including an SPI interface) that would be available for the near term but couldn't find anything.


Any thoughts or suggestions would be most appreciated. 




Joe Burch