Design Guide

Hardware Interfaces
A DIVISION OF TRIMBLE
Hardware Overview 27
TTL Level UART Interface
Only three pins are required for serial communication (TX, RX, and GND). Hardware
handshaking is not supported.This is a TTL interface; a level converter is necessary to
connect to devices that use a 12V RS232 interface.
The RX line is a 3.3 volt logic CMOS input and is internally pulled up with a resistance
value of between 20 and 60 kOhms (40 kOhms nominal). It must be low before the
module is turned off and low before the module is turned on. This can be insured if
interface drivers are used that are powered by the module itself, as shown in the interface
board example.
The connected host processorʼs receiver must have the capability to receive up to 256
bytes of data at a time without overflowing.
These are the baud rates supported on the interface (bits per second):
– 9600
– 19200
– 38400
– 115200
– 230400
– 460800
– 921600
Note
Upon initial power up, the default baud rate of 115200 will be used. If that
baud rate is changed and saved in the application mode, the new saved
baud rate will be used the next time the module is powered up. (Check the
firmware release notes to confirm that saving of settings is supported.)
General Purpose Input/Output (GPIO)
The four GPIO connections, described in the ThingMagic Nano Digital Connector Signal
Definition, may be configured as inputs or outputs using the MercuryAPI. The GPIO pins
should connect through 1 kOhm resistors to the module to ensure the input Voltage limits
are maintained even if the module is shut off.
Module power consumption can be increased by incorrect GPIO configuration. Similarly,
the power consumption of external equipment connected to the GPIOs can also be
adversely affected. The following instructions will yield specification compliant operation.
On power up, the ThingMagic Nano module configures its GPIOs as inputs to avoid
contention from user equipment that may be driving those lines. The input configuration is