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[wxsig] RE: Replacing the MX614 with TCM3105

William Beals will at beals5.com
Thu Feb 15 04:07:53 UTC 2007

I did look up the specifications of the two chips and think it is a bit more
involved.  You are correct about the /RDY and clock pins, but the reason
they exist on the MX614 is that the interface is synchronous serial.  In
other words, the 6808 can send the data to the MX614 without any timing
constraints other than to the clock pin.  The data does not have to be
sent/received at exactly 1200 baud.  Additionally, the MX614 signals there
is data ready by asserting /RDY.  The 3105 is an asyncrhonous serial
interface. As such, no clock or /RDY pins are needed, but the data being
sent must be very accurately timed to exactly 1200 baud--just like a UART.
In fact, the 3105 does require a UART interface.  The T238 is using that
interface for other purposes now, but it could be repurposed.
There is a bigger issue too, one that forced me to abandon even the hardware
synchronous serial interface for the MX614 and do all of the data formatting
in software.  The APRS protocol does something called bit-stuffing.  If
there are more than five zeros in a row, a single 1 bit is inserted into the
stream.  This means that very quickly, bytes of data being transmitted are
no longer byte-oriented for a hardware-based transmitter.  Details of this
are covered in the APRS protocol specs and commented to some extent in the
mx614.asm source code.


From: huys cobb [mailto:huys_cobb at yahoo.co.id] 
Sent: Wednesday, February 14, 2007 12:46 AM
To: wxsig at lists.tapr.org
Cc: will at beals5.com
Subject: Replacing the MX614 with TCM3105

Thank's all
Mr. William,Jhon and Michael

I think the only problem was /RDY(pin 15) and Clock(pin
12) that totally different between MX/FX614 and 3105.
the Clock of 3105 used for type of baud rate
operation,clock of 614 using for timing recieve.
/RDY didn't exist at 3105,this signal for ready to
recieved the uC.

Perhaps,maybe only with minor modification between that in
T238+ code?

Thank's all
Huys Cobb


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