8251 troubles

[dwight elvey]

> Date: Mon, 28 Apr 2008 13:22:08 -0800
> From: hilpert at cs.ubc.ca
> To: General at priv-edtnaa03.telusplanet.net
> CC:
> Subject: Re: 8251 troubles
>
> dwight elvey wrote:
---snip---
>>
>> DI
>> CALL SETUP
>> ; .DB $01F ; 9600
>> ; .DB $01D ; 4800
>> .DB $01B ; 2400
>> ; .DB $019 ; 1200
>> .DB $0AA ; SYNC
>> .DB $0AA ; SYNC
>> .DB $040 ; RESET
>> .DB $0CE ; 2STOP, NO PARITY, 8BIT , X16
>> .DB $010 ; CLEAR ERRORS
>> .DB 0
>>
>
---snip---
>
> I have the datasheet for the 8251A but not the 8251 here, so just some guesses:
>
> - perhaps the 8251 (as opposed to the A) requires the receiver to be re-enabled
> (not a full reset) after receipt of each character (an 'explicit ack') (?).
>
> - .. check the error flags to see if a framing error is occurring?
>
> - .. try sending a stream of (best random) characters at full rate,
> as opposed to just 2 manually? This might get around some framing
> inconsistency or such to at least see if a subsequent character can be received.
>
> - (may be inconsequential, but in the init sequence the two sync characters
> are not preceded by a mode byte (perhaps SETUP does this internally?))

This is the perscribed way to get around another feature. If the 8251 was in
the middle of a read sync sequence, one should first send 2 dummy
command/sync. It will then be sure to be waiting for a command.
Sending a reset command enables it to look for the mode. The
$0CE is the mode to select async and dividers and such. Anything that
then follows is a command.
 I'll try resending the recieve enable to see if that makes a difference.
Dwight


_________________________________________________________________
Back to work after baby–how do you know when you’re ready?
http://lifestyle.msn.com/familyandparenting/articleNW.aspx?cp-documentid=5797498&ocid=T067MSN40A0701A