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Re: [N8VEM-S100:2605] Re: A new (V2) version of the S100 Bus System Support Board

I think I understand the EEPROM trick, with my poor mechanical engineer brain.  If my two months of digital logic self-study are correct, you're making a chip with several state machines programmed into it, where the S-100 address lines connected to the 4 EEPROM lines select which state machine is in operation and the counter goes through the steps to output the corresponding sequence to I2C to send the data.  A neat trick.  

On Tuesday, March 4, 2014 2:14:47 PM UTC-8, Vince Mulhollon wrote:
On Sunday, March 2, 2014 11:52:02 PM UTC-6, monahanz wrote:

I have not found any individual OLED displays that latch and display Hex codes.

One (e)eprom with some peculiar programming and a 8-bit or 16-bit free running binary counter driving the LSB of the address leads and a latch sample input driven from D0 of the eprom and D1 drives the reset of the otherwise free running counter.  The MSB of the eprom address is the data output from the latch, probably just a couple bits.  The D2-D7 (however many needed) blindly holler out I2C or SPI signals, sure hope there's a LCD there to listen.  At the end of the blindly hollered out canned SPI/I2C message you clear D0 for awhile to latch in the new MSB for next cycle, and then whack D1 after some time to start the whole madness over.

Some displays get all wound up about getting initialized / reloaded over and over.  Of course if you've got the dough, just use a bigger eeprom and slower clock, assuming you can tolerate the latency, so it only reloads the display once a second or whatever seems about right.

Takes a modest sized (e)eprom, a chip or two for the 8 or 16 bit counter, a latch, and not much else....  pull up resistors for the I2C I guess, along with the LCD (or OLED in this case).

I would suggest that the smarter the device, the harder it is to pull this crazy design off.

I've done this with one message using an old LCD a long, long time ago.  Only needed 4 chips and an oscillator and made a LCD display say "hi".

Filed under dumb eprom tricks, I guess.  Its a derivative of the old "hook up a D/A to generate sounds" trick.  Works well if you only need a couple sounds.

Now a days you'd probably use a 75 cent custom programmed PIC.  I think this could get away with the 8 pin dip 10F series if you use I2C thats 2 pins and 4 pins of input data and 2 pins for power and use the internal clock.