4.1 General I/O Information

The SHA104-TFLXAUTH operates as a client device and utilizes a single‑wire digital serial interface or I²C to communicate with a host controller. The host device controls all read and write operations to the client device(s) on the serial bus. The protocols are selected by specifying the part number that is ordered:

• Single-Wire Interface: Uses a single GPIO connection on the system microprocessor that is connected to the SDA pin on the device. The interface is compatible with Microchip AT21CS01 and AT21CS11 in High-Speed mode. It permits the lowest number of pins connected to any removable or replaceable entity. The bit rate is variable with a maximum achievable bit rate of 125 kbps. SWI can be operated in Parasitic Power or Direct Power mode. Multiple client devices are permitted when the client device is powered directly. Only one single-wire client on the interface is supported in Parasitic Power mode.
• Single-Wire Interface – Parasitic Power Mode:In parasitic power mode the device is charged through the SWIO Signal. It is recommended that the host micro have a totem pole CMOS output driver. Whenever this output is High, the SHA104-TFLXAUTH will charge the C1 capacitor if the voltage of V_{CC_DVC} is less than V_SIO. Internal circuitry will prevent this charge from being bled off when the SWIO signal is driven low. This signal must be driven High during the write phase or calculation phase of any command. The host microcontroller is providing the needed power for the device to operate. The internal circuity will allow for the V_{CC_DVC} to be charged to the V_SIO level. In a normal application, this will be the same as the V_PUP voltage. V_PUP is the supply voltage on the high side of the R_PUP pull-up resistor. When data is being read from the SHA104-TFLXAUTH device, the host micro I/O will be placed into an input mode. The SHA104-TFLXAUTH device will pull the signal low and the R_PUP resistor will pull the signal high as required.

• I²C Interface: 
This mode is compatible with the I²C standard and with the Microchip AT24C16 Serial EEPROM interface. Two pins, Serial Data (SDA) and Serial Clock (SCL), are required. The I²C interface supports a bit rate of up to 400 kbps.