Quickest way to do an If val1 = val2 with Word variables

[bcd]

Hi Guys,

So I finally got some time to do some testing.

I have an admission to make - the 60uS I was seeing that started this whole process off seemed to be caused by failing to set my debug output that was watched with the logic analyser to a known state if the values didn't match...

What I did yesterday was run a few different comparison scenarios to see what sort of timing you got. Remember this is a 16f1933 running at 32Mhz, so instruction time is about 0.5us.

What I am doing is comparing the address I want to grab with the current position in the incoming data stream. I reset a counter when I see a header and then count each data packet coming in. When the address matches the count I receive the next three values into a buffer that the main code loop processes. The address can be a value from 1 - 512 so I need to use word variables.

Doing an if..then compare with two word variables takes 5.125 us

dbg_out = 1 ' set my debug line high for timing test
if current_position = current_add then

' do the buffer loading

endif
dbg_out = 0

Doing an if..then highbyte and lowbyte compare takes 2.125us

dbg_out = 1 ' set my debug line high for timing test
if current_position.highbyte = current_add.highbyte then   ' 2.125 us
  if current_position.lowbyte = current_add.lowbyte then 

' do the buffer loading
 endif
endif
dbg_out = 0

Doing an XORNOT compare takes 4.125us

dbg_out = 1 ' set my debug line high for timing test
if (current_position XORNOT current_add) then

' do the buffer loading

endif
dbg_out = 0

Doing an XORNOT Lowbyte Highbyte compare takes 7.625us

dbg_out = 1 ' set my debug line high for timing test
if (current_position.highbyte XORNOT current_add.highbyte) then
 if (current_position.lowbyte XORNOT current_add.lowbyte) then   

' do the buffer loading

 endif
endif
dbg_out = 0

So it looks like Darell was correct that the fastest way is a If..Then with Lowbyte / Highbyte.

Bill.