11 Mar
2007
11 Mar
'07
5:22 a.m.
On Sun, 11 Mar 2007, Dave Dunfield wrote:
I'm not very keen on microcontroller hacking. Which one would you
recommend for something like this? I'm guessing that for a fixed-speed
job, you'd have the microcontroller, two MAX232 chips, and not much else.
--
David Griffith
dgriffi at cs.csubak.edu
A: Because it fouls the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?
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.