8251 troubles

[dwight elvey]

> From: cclist at sydex.com

> Date: Sun, 27 Apr 2008 08:23:09 -0700
> From: dwight elvey 
>
> I'm going to assume that you have an 8251A, not an 8251. If the
> latter, either sell it to a collector or have it bronzed and made
> into a tieclasp. There are substantial differences between the -A
> and non-A parts, all annoying.

Hi Chuck
 The chip is a NEC 8251C.

>
> Glancing at your code, I'm a bit puzzled by the final initialization
> byte of 0x10. Why isn't this, say, 0x37? Why would you disable the
> receiver? 8251A commands are bit-inclusive; that is, ALL bits in the
> command register are interpreted independently of one another. Thus,
> 0x10 sent to the command register doesn't just reset the error flags,
> it also disables the transmitter and receiver and drops DTR and RTS.

 I'd originally done a 37 but looking at some example code,
I thought I'd try separating out that bit. No change in results.
The data sheet seems to indicate that the flags will not effect
or stop operation.

>
> The implication is that since the command register's write-only, you
> have to remember the last command you sent if you want to reset the
> error flag. One of the minor annoyances of a few early Intel
> peripherals.
>
> Anent that last one--make certain that your handshake lines
> (RTS/CTS/DTR) are set to the proper levels--an inactive CTS will
> prevent the 8251A from transmitting.

 At least at the port, there is no change. There could be something
at the chip. Since I've not even gotten to the sending serial, yet, CTS
isn't yet an issue.

>
> Hope this helps,
> Chuck
>

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