PCW's 25 worst tech products of all time

[Michael B. Brutman]

Your intimate knowledge the machine machine betrays a deep, but 
forbidden love for it. ;-)


Tony Duell wrote:
>> A bigger shortcoming that I should have mentioned was having the 
>> keyboard using the NMI interrupt instead of IRQ1.  I forget the exact 
>> reason for this, but it resulted in a lot of lost keystrokes an annoying 
>> beeps.
> 
> 
> There was a reasonable reason for this. 
> 
> The PC keyboard is farily hardware-intensive. The keyboard sends a serial 
> data stream that goes into a shfit register on the PC mainboard. When a 
> character has been received (IIRC), ther hardware generates an IRQ1 and 
> holds the keyboard clock line, preventing the keyboard from sending 
> another character until the first one has been read by the 8088
> 
> The PCjr keyboard is software-intensive. Whether you use the IR link or 
> the cable, the serial data stream is decoded by the 8088, there is no 
> shift register on the PCjr mainboard. Also, in the PCjr, there's no way 
> to tell the keyboard to stop sending because the main processor hasn't 
> read the character yet. 
> 
> Therefore in the PCjr, you need a high-priorty interrupt (i.e, NMI) which 
> is generated when the keyboard sends a bit, The 8088 takes over then, 
> reads in the character from the keyboard and processes it. Otherwise 
> you'd loose or mangle an awful lot of keypresses.
> 
> -tony
> 
>