baud modifier

Dave Dunfield dave06a at
Sun Mar 11 06:40:13 CDT 2007

> I'm thinking of a device that would step down the speed of an rs232
> connection from, say, 9600 to 110.  The idea is to allow a computer that
> can't do 110 to talk to an ASR33 teletype.  Does such a device exist?
> What's it really called?  Does anyone have any schematics for one?

I have devices that will do this - these are actually RS-232 data switches
that I designed in the 80s. It was a whole line ranging in size from 8 to 56
ports, once a connection is made, the ends operate with independant
interfaces, and the switch mediates between them.

For what you want to do you only need two ports. You will also need either
some kind of flow control (RTS/CTS, XON/XOFF etc.) on the faster speed
port, or a buffer large enough to contain the maximum possible data block
that will be sent to the slower-speed port before the system waits for a
response from it.

Easy to design and build - a single-chip micro with two serial ports would
fit the bill nicely, otherwise you could bit-bash the slow speed port, or
use an external UART. Simply set the speed/parity/Dbits/Sbits that you want
for each port, then copy data between them through buffers - when a buffer
approaches full, assert flow control on the filling port, when the buffer
later approaches empty, deassert flow control on the filling port.


dave06a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools:
com             Collector of vintage computing equipment:

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