Re: T or F questions

Ed Casas (edc@ece.ubc.ca) Thu, 13 Apr 2000 22:54:14 -0700 

Date: Thu, 13 Apr 2000 22:54:14 -0700
From: Ed Casas <edc@ece.ubc.ca>
Subject: Re: T or F questions



On Thu, Apr 13, 2000 at 08:04:18PM -0700, Xin Sun wrote:

> Are these ... answers [below] correct?

> (T) A register must be used to implement a parallel input port.

No, F.  A tri-state buffer is used to implement an input port.
See your lab.

> (T) To ensure reliable commucications a DCE should always be
> connected to a DCE and a DTE should always be connected to a
> DTE.

No, F.  For example, a DCE won't talk to a DCE because, for
example, both TxD signals will be inputs

> (T) No CPU time is used by an interrupt-driven input interface
> while the device is not is use.

True.  If the ISR is not executed, no CPU time is used up.

> What minimum number of bytes must be left free on an appliation
> program's stack on an IBM pc to allow interrupts to execute and
> return properly?  the answer is 3.

No.  3 words are pushed (flags, CS and IP), but that is 6 bytes.

-- 
Ed Casas   edc@ece.ubc.ca   http://casas.ece.ubc.ca   +1 604 822-2592