XR88C681CP Datasheet, PDF (20/99 Pages) Exar Corporation – CMOS DUAL CHANNEL UART (DUART)

XR88C681
one or two characters are still remaining in RHRA, following
data reception. Hence, it is possible that the last two char-
acters in a string of data (being received) could be lost due
to this phenomenon. Therefore, the user is advised to read
RHRA until empty.
ISR[0]: Channel A Transmitter Ready
 (% ( (%  $(' + 5G "  NO
 (% ("   %" ( $('%   8 (% &  $ (%
$&  ''  ' ' +  
,   ( (%
'$    
, (%   ' '  8 L
 $ (% % -( "     ' ' (%  %+$   
 5G (% %      %( (% ( ((&
 $  $ (% '$      %( (% $(%$

'% $$ (  8  (    %( (%
$(%$ (    %($
C.2 Interrupt Mask Register (IMR)
  #  %3 -(% (%  CB(  &D -(%
 ('  %   %  %'   ' $(( %   (
'%      (%%  #  E%   
'%% #   $%"   % %   ( +
%3( -  '3( - '( ' $(( % + '%( -  
   (%%  #  E%  +"  
(+ +   # (% %% (&   % %   #
8" + ' %%"   *(  +   # (%
% $ 
Bit 7
Input Port
Change
 J ++
 J 
Bit 6
Delta Break
B
 J ++
 J 
Bit 5
RXRDY/
FFULLB
 J ++
 J 
Bit 4
TXRDYB
 J ++
 J 
Bit 3
Counter
Ready
 J ++
 J 
Bit 2
Delta Break
A
 J ++
 J 
Bit 1
RXRDY/
FFULLA
 J ++
 J 
Bit 0
TXRDYA
 J ++
 J 
Table 6. IMR Bit Format
#+   % (% %     '( ( " .% 
% $ (  CD    ( ( (   #" '% $( -
   # 
 $((  9(3(%"  $(%  %3
  '( ' $(( '%( -  ( "   %
% $ (  CD    ( '( '% $( -   
' $((      ( %   % $ (
/ ^{ CD%   (% -(%%}
Please note that IMR is a Write Only Registers, and can
therefore not be read by the processor.
C.3 Masked Interrupt Status Register (MISR)
  '   +   # -(% (% %('&   %% +
7( -   #  $ # - 
#
   J N#
  %O  N#
  %O
  ((( +   #  (' ( %  
&  $( -   # (%     (% ( (   # '
-- C (- D $   ( '% $( - ' $(( %
      &   $ &   #  +"
  %" +( - $( -   #  % -(%"
(   3 (%( % +L  $ !'  C(&(D
7 +   #  $ # '  % ( '   # (% 
CB(  &D -(%  $ '   $ &   '%%"
  '  % +   # (    %$ ( %&%
&" +  '   $$((  $  $
%+  $ E($  %  (% '((& ' 
(( $ ( % +   #
C.4 Interrupt Vector Register, IVR
 (% -(% (%  & %$ + #  ;' - (
      (% ' $$ (    %'( ?$
B ( (  (% $"   '  % +   #; (% &('&
$    %( - $$%% +    % # 
(' (   (%" (   #$" # 
;' - ( (% &('& +$ ++' ( B 
    (% ( - (   #$"   #; ' 
%$ % -  % $.( -(%%    +
  #;"  (     (% ( - (   ?$ (%
% $ ( Section C.6
C.5 Limitations of the DUART Interrupt Structure
  #  ' ++$ &     %  
%  -      -  ( % (
% %  '( 8  $ 8  #  ' $(( %L  

 .( $& ' $(( "  $  '  -% (  
*3
 $((    '( 8" %($ +
  C *3
 $(( D *"    H% # 
' $%   + (  E%% $