KayPro II keyboard schematic

Tony Duell ard at p850ug1.demon.co.uk
Thu Dec 20 15:47:50 CST 2007

> > From: "Andrew Lynch" <lynchaj at yahoo.com>
> > Does anyone have a schematic for *simple* hardware only circuit using a
> > commonly available UART, like an 8251 or 8250, to do the serial to
> > parallel conversion?  I am looking for a schematic which I can easily
> > modify to strap the UART to 300bps operation.
> If you don't want programmable logic, an 8251 or 8250 isn't going to 
> be what you want.  Try a TR1602 or TR1865 or any of the other 

Actually I have seen a device that used a 8251 USART and set it up using 
a little counter/state machine to load the control registers from DIP 
switches (and some fixed bits of course). IIRC that chip has the TcRdy 
and RxRdy signals brought out to pins, when the latter was asserted the 
hardware read out the Rx register, etc. 

I don't think there were any PROMs in that design. Certainly no 
microcnotrollers, PALs, or anything like that.

I _think_ it was athe HP9836 RS232 interface for the 9825, but I might be 
confusing it with something else.

> "hardwire" UARTS--set parity, data bits, etc. by connecting 
> appropriate pins to Vcc or GND; put the serial data in on one pin and 
> take the parallel data out on 8 pins.  No programming needed.

Oh, indeed. That's a much simpler drvice to sue, and a better choice here.


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