Is it possible to connect 2 TTL serials directly or is this going to fry something? How about between two Maple's? (And of course making TX->RX / RX->TX )
Ian
Connecting two TTL serial I/O's directly
(9 posts) (3 voices)-
mikep
Member"TTL" usually implies 5V logic, 3.3V devices usually use LVTTL, which has lower voltage levels.
Some of the STM32/Maple pins are 5V-tolerant, see here:
http://leaflabs.com/docs/gpio.html#pin-mapping-mega-table
So the USART1/USART3 pins are 5v-tolerant, but USART2 pins are not!Even when using a 5V tolerant pin, I usually put a resistor (about 1k) into the Rx and Tx lines, just in case you hook the two Tx lines together accidentally. You should not need a voltage divider or level shifter: a voltage of <0.8V equals "0" in LVTTL and in TTL. And the "1" voltage in LVTTL (>2.4V) should be recognized by standard TTL as a "1" as well. Nice diagram here:
http://www.interfacebus.com/voltage_LV_threshold.htmlSo you can hook 2 Maple's together without problems, but I would still recommend the 1k resistor for the same reason: if you accidentally connect the two Tx lines and they are both using push-pull output mode you can fry the outputs.
Posted 5 years ago # -
gbulmer
Moderator"TTL" usually implies 5V logic, 3.3V devices usually use LVTTL
I try not to ASSuME too much :-)
FTDI USB to serial cables are described as TTL, but are sold in 5V and 3V3 versions.
http://uk.farnell.com/ftdi/ttl-232r-3v3/cable-usb-to-ttl-level-seri-converter/dp/1329311
Posted 5 years ago #
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