Some digital content

[Don Tillman]

   Date: Fri, 11 Apr 1997 12:40:21 -0600 (CST)
   From: POLARIS at VAX1.Mankato.MSUS.EDU

   I know this may be strechting the limits of synth-diy's charter a bit, but..

Digital is completely fine for this forum.  Perhaps you were thinking
of Analogue-Heaven?  Nah, AH is reserved for boasting about how much
you paid for your synth.  

   I'm designing a digital sequencer for my modular which uses a 2k x 8bit
   SRAM chip (2016, I think) and A/D and D/A converters.  The part that
   has me consfused is how to display the address number on a 4-digit
   LED readout.  It will be an 11-bit binary number, and I've only
   seen BCD-to-seven-segment decoders, not something to convert big binary
   numbers to multi-digit displays.  

Some early Roland synths (the Compuphonic?) had to deal with the same
problem -- they had their patch numbers count in one-based octal (1,
2, 3, 4, 5, 6, 7, 8, 11, 12, 13, 14, 15, 16, 17, 18, 21, 22, ...).
Apparently their engineers didn't know how to convert from binary to
decimal. 

The "painstakingly proper" approach would be to build a binary-to-BCD
converter which would work arithmetically the same as you'd do it by
hand.  I think there are some CMOS chips available that do this four
bits at a time.

A far more practical approach is to just use BCD counters to address
the SRAM, 11-bits counting from 000 to 799, wasting off a fraction of
the memory.  Not enough for you?  Use larger SRAM, it's dirt cheap.

  -- Don