Dear Dan,

I found the following message at Phillips MCU forum, may be helpful for you.

From: "Yamkovoy, Paul" <yamkovoyp@rd.simplexnet.com>
To: forum@ibsystems.com
Subject: RE: Manchester encoding
Date: Thu, 29 Apr 1999 18:00:15 -0400

Manchester code (sometimes also called a split-phase code) eliminates
the DC component from your data stream and significantly reduces
low-frequency components, regardless of the data sequence.

Using Manchester code: "1" is represented by a positive pulse followed
by a negative pulse. Both pulses are of the same amplitude and half-bit
wide. For "0" the polarities of these pulses are reversed.

It is not possible to generate Manchester Code using standard UART.
You may do it with 2 I/O lines driving unity gain differential amplifier
(buffer).

Here is example:

I/O line1 connected to the "+" input of the diff amplifier
I/O line2 connected to the "-" input of the diff amplifier

To transmit "1":
set I/O line1 for half bit time, same time I/O line2 must be at "0" ,
clear I/O line1 and set I/O line2 for the second half of the bit time.

To transmit "0":
set I/O line2 for half bit time, same time I/O line1 must be at "0",
clear I/O line2 and set I/O line1 for the second half of the bit time.

As a software solution you may use somewhat modified
"software UART".

Thanks.

Paul G. Yamkovoy
Principal Engineer, Hardware design.
Simplex Time Recorder Co.

yamkovoyp@rd.simplexnet.com