Sources for 8b TTL keyboards (Keytronics)

Chuck Guzis cclist at
Sun Dec 7 13:42:25 CST 2008

On 7 Dec 2008 at 18:44, Tony Duell wrote:

> Can you program and debug either or both of these chips without 
> propietary hardware or software. In other words, is documentation for the 
> following availalbe (without signing an NDA, etc )

Absolutely.  Many of the tools are open-source, royalty-free, running 
on a variety of OS platforms.  The chips themselves are documented to 
a fare-thee-well.  For example, the ATMega8 user's manual runs to 
over 300 pages (PDF downloadable for free) and it doesn't even 
discuss the instruction set--that's in the "AVR family" manual.

> 1) How to send/receive words to the chip (what lines to wiggle and how, 
> what voltages to apply, etc)
> 2) The binary instruction set 
> 3) THe debugging commands/responses

Yes, all of that, provided that you're working with a chip that has 
onboard breakpoint capabilities (not all do).  

When checking out a new circuit, I use a little debugger that I wrote 
myself for the AVR that communicates over an RS-232C serial port (I 
had to add a MAX202 to provide EIA voltage levels).  It allows me to 
twiddle bits on various ports and on-chip devices to see what 
happens.  It took me about 2 days to learn the instruction set and 
write the debugger.  It worked on the 2nd try.  

Even if you're reduced to "cut and try", programming is usually very 
fast and can be done in-circuit.
> Could I, if I wanted, make the programmer and write the software from 
> scratch?

Many people in fact, do just that.

Here, for example, is one parallel-port in-circuit programmer for the 

It is by no means the simplest, requiring one 74HCT245 to work.  If 
you want to write your own programming software, the manual documents 
the protocol.

Similar devices and documentation exist for the PIC uCs.

uCs are simple, cheap and ubiquitous.  They're even "vintage." It's 
just plain silly to eschew them.


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