Erronous MuP21 schematic?

Andrew Sieber (kd4jtv@bbs.wa4yse.ampr.org)
Fri, 15 Nov 1996 22:18:41 -0500


According to the MuP21 manual, the WE pin on the processor
is                   
low for a write operation and high for a read.  On page 92
a                    
system schematic is shown with this pin connected straight
to                   
the direction control pin of a 74245.  The way the
schematic                    
is drawn, it appears that during a read operation addresed
to                   
the 74245, neither the processor nor the '245 will drive
the                    
bus.  However, during a write, both will!  This can't
be                        
what is intended.  Am I reading the schematic wrong, or is
it                   
backwards?  I'd like to know before I build a system, else
I                    
might destroy my MuP21 when it and the '245 fight for
control                   
of the bus.  I haven't done an exhaustive search, but I did do
a quick check through the MISC archives and didn't notice
anything on this topic.  Any clarification would be appreciated.
--Andrew Sieber
kd4jtv@bbs.wa4yse.ampr.org