In SX Microcontrollers, SX/B Compiler and SX-Key Tool, George Herzog wrote:

Hello,
Yes,
The easiest way to do this is to drop the parity bit on the output going into RS-232. But in that case, I still need to ADD the parity bit to input to the keyboard from the RS-232.  [I suspect IBM intended to make this a very difficult interface to duplicate]

There is always the possiblity that one might want to preserve the parity in this or a future project, have the destination verify it, and make requests to resend.  

I suppose here it would best best to just trap it as an error and immediately ask for the keyboard to resend its output to the SX.  But still, that requires one to recalculate parity and compare it.  It certainly would simplify the RS-232 output.  Adding a 9th bit is a big project. 

Seems impossible to do without a parity calculation in at least one direction, if not both.

I took a look at Peter V's code and was quite surprised by the way parity is calculated - boolean logic rather than a simple iteration of XORs.  It seems there are at least 4 ways to do this.  I guess this saves program space and time.

BTW< I got all four parity calculation examples at http://www.sxlist.com 
That is where Peter V. posted his code and made reference to his source for parity code.  

Seems that I have been ignoring an excellent resource for SX SASM code examples.  Everyone should try SXLIST for more support.

Daniel,
Jan Axelson has several good books.  I noticed yesterday that all are ON SALE at Amazon.  I am more interested in her Ethernet text.
I may at times seem pedantic too, but it is exactly because there are others that might be struggling with similar issues, but not jumping in.  If I look only at who is logged on, I begin to think I am one one of maybe 10 beginners to SASM.  I am sure that isn't the case.

---------- End of Message ----------


You can view the post on-line at:
http://forums.parallax.com/forums/default.aspx?f=7&p=1&m=110792#m111050

Need assistance? Send an email to the Forum Administrator at forumadmin@parallax.com

The Parallax Forums are powered by dotNetBB Forums, copyright 2002-2006 (http://www.dotNetBB.com)