#05, M1S: RS485 Port
Function: RS485 port with half-duplex operation
Form factor: M1S
Category: Input/output module
Special needs: [SER]
Power requirements: 5V/15mA
This serial port offers a single pair of +/–485 lines. Hence, it can only communicate in half-duplex mode.
Direction control is through the RTS line — the line must be LOW for data input (data flowing into the host Tibbo Project PCB) and HIGH for output.
The original version of this Tibbit made no use of IO3 and IO4.
Revision B of this Tibbit provides 5V power on IO3 and GND on IO4. There is also an onboard 120Ω termination resistor (0402 package) between the +/–RS485 lines. This resistor was added for the convenience of users.
Revision B devices are marked by a small round sticker with the letter "B" on the side of the Tibbit.
There are three LEDs: two red and one green. The red LEDs are connected to the TX and OUT/–IN outputs. The green LED is for the RX input. All LEDs are buffered (with logic gates) and light up for the LOW state of their respective lines.