m5stack ATOMIC DTU NB-IoT2 Global Version v1.1 (SIM7028)

AI context

Dense context for pasting into a model prompt — addresses, pinout, voltages, tolerances and the vendor's reference circuit.

PART: M5Stack Atom DTU NB-IoT2 v1.1, SKU A106-V21, a 64.3 x 24.0 x 28.7 mm (30.0 g) DIN-rail carrier for an Atom series controller around a SIM7028 Cat-NB module. The Atom itself is NOT included. It adds an M5IOE1 IO expander, an RS485 transceiver and a 9-24 V supply. The title carries the module, so part is null.\nADDRESSES: none published. The M5IOE1 expander sits on the Atom's I2C bus (nets IIC_SCL/IIC_SDA on the schematic) but the vendor publishes no address for it, so none is recorded.\nPINOUT: the Atom's 9-pin bottom interface, as the vendor's own PIN | LEFT | RIGHT | PIN table prints it: pad 1 3V3, pad 2 PORT.A, pad 3 NBIoT2_UART_RX, pad 4 PORT.A, pad 5 NBIoT2_UART_TX, pad 6 5V, pad 7 RS485_TX, pad 8 GND, pad 9 RS485_RX. The modem's UART and the RS485 transceiver share the same nine pins, which is why the table labels PORT.A on pads 2 and 4.\nSUPPLY: 9-24 V into the HT3.96R-4P RS485-style terminal block; the board makes its own 3.3 V (TPS7A2033PDBVR regulator on the schematic) and passes 5 V to the Atom on pad 6. It can also feed the Grove port at 5 V up to 1.3 A from the RS485 supply. Published draw: 24 V at 9 mA with the modem powered off, 5 V at 8.82 mA standby, 5 V at 43.91 mA continuous TX/RX.\nLOGIC: 3.3 V on the Atom interface and on the modem side; the RS485 A/B pair is the transceiver's differential output, not TTL. 115200 bps 8N1 to the SIM7028, per the specification table.\nCIRCUIT: the RS485 side is an SP3485EN-L/TR (U5) with A/B brought out to the HT3.96R-4P terminal (nets RS485_A / RS485_B, with R19 4.7 kOhm and R21 10 kOhm on the pairs); the modem's UART has R11 22 Ohm series resistors; the 3.3 V rail is decoupled with 1 uF/16 V and 100 nF parts and the 9-24 V input has 10 uF/50 V and 22 uF/10 V capacitance with a 200K/1% + 13K/1% divider. Power gating and reset of the SIM7028 are done through the M5IOE1 expander rather than direct GPIO, and the expander also samples the module's power status on an ADC input.\nTRAPS: (1) The Atom is not included in A106-V21 - the earlier A106 shipped one, this one does not, so the pin table describes the socket, not a working unit. (2) Modem power enable, reset and status monitoring are on the IO expander, not on the Atom's own GPIO, so firmware has to drive the expander before the modem will answer. (3) The RS485 port is also the power input - a two-wire 485 bus and a 9-24 V supply share one terminal block. (4) The modem is Cat-NB only (bands B1-B28/B66/B70/B85); there is no 2G/4G fallback.