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Sheet 10/10 · Serial buses tee
TX → RX. Always Crossed.
UART, TWI and SPI side by side on one tee: wire counts, signal names, the crossed TX/RX, pull-ups and chip selects, with the ATmega328P pins for each bus.
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On the shirt
What it teaches
- UART needs two wires and ground, and TX always goes to the other side's RX. Wire TX to TX and both sides talk into the same line, so nothing arrives.
- TWI (the 2-wire bus, SDA + SCL) needs one pull-up resistor per line, and its 7-bit address space allows up to 128 addresses on those two wires.
- SPI uses four wires: SCK, MOSI, MISO, plus one SS (chip select) line for every chip on the bus.
- On the ATmega328P: TXD/RXD are PD1/PD0 (D1/D0), SDA/SCL are PC4/PC5 (A4/A5), and SCK/MOSI/MISO/SS are PB5/PB3/PB4/PB2 (D13/D11/D12/D10).
Sources
Where every fact comes from
The shirt
Fabric, fit and printing
Bella+Canvas 3001 unisex tee: combed and ring-spun cotton (heather colours are a cotton/poly blend), printed direct-to-garment and made to order.