15 Nov
2019
15 Nov
'19
1:12 a.m.
On 2019-Nov-14, at 10:23 PM, Jim Brain via cctalk wrote:
If you look at the values received by an 8N1
connection from a sender using the different settings, you get:
AT
at
At
aT
7E1
E174
41D4
E1D4
4174
7O1
61F4
C154
6154
C1F4
7M1
E1F4
C1D4
E1D4
C1F4
7S1
6174
4154
6154
4174
8N1
6174
4154
6154
4174
Obviously, still trying to find the magic boolean logic equation to tease out the parity,
but you could brute force it with these values and only aT would cause you issues
requiring looking at CR (7E1 would send 8d, while 7S1/8N1 would send 0d.
(If it is of any consequence at this point)
If those vertical groups of 4 are intended to correspond to the first group of
AT/at/At/aT, then you have the case bit (0x20) inverted, uppercase are bit 0x20 OFF (lower
value), lower case are 0x20 ON (higher value).
If it's of any interest, here's some (untested) code, using your finding that the
case must be consistent:
===============================================
/* Return: -1 the two characters are not ASCII A/a and T/t
* -2 the case is not consistent between the two characters
* 0 SPACE parity
* 1 ODD parity
* 2 EVEN parity
* 3 MARK parity
*/
int
AssessATParity( chA, chT )
int chA, chT;
{ int pp;
if( (chA&0x5F)!='A' || (chT&0x5F)!='T' ) // check characters are
A/a and T/t
return( -1 );
if( ((chA^chT)&0x20) != 0 ) // check case is consistent
return( -2 );
pp = ((chA&0x80)>>6) | ((chT&0x80)>>7); // extract and combine the
two parity bits into two-bit value (0..3)
if( pp==0 || pp==3 ) // check for Space or Mark parity
return( pp );
return( (chA&0x20) ? pp : (3-pp) ); // Odd or Even parity, but pp value (1 or 2)
must be swapped depending on case
}
====================================================