Question about modems

[Jim Brain]

On 11/15/2019 3:12 AM, Brent Hilpert via cctalk wrote:
> 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).
Well, the above values are what an 8N1 connections sees when the other 
end is set to the various 7 bit parms.  I verified that the numbers 
above are correct, case and all.

Let me peruse the code you sent.  I did some eoring, but maybe your math 
works as well.  First, it looks like I need to replicate the behavior os 
the at prompt (it looks to be calculated as soon as the T is received).

Jim

-- 
Jim Brain
brain at jbrain.com
www.jbrain.com