Designing Cascaded I2C Multiplexer Topologies for High Density Hardware
Cascaded I2C multiplexers resolve address collisions in high-density systems by isolating bus segments, requiring strict RC capacitance and switch resistance control.
PCA9544A
Interrupt Handling
Industrial control systems require bidirectional switches to manage multiple sub-branches of a two-wire serial interface. The PCA9544A operates as a four-channel multiplexer controlled via the I2C bus, featuring interrupt logic to alert the master of downstream events. When an active device on a downstream branch generates an interrupt signal, the chip registers it and asserts its own interrupt output to notify the system host.
This allows the host controller to immediately identify which downstream branch generated the alert.
Address Resolution
System architectures with multiple identical I2C devices utilize a multiplexer to solve address conflict issues. The chip routes the clock and data lines of the master bus to one of four downstream pairs. By executing a write command to the internal control register, the master selects the active channel.
Since only the selected channel is electrically connected to the bus, identical slave devices on different channels can share the same physical address without interference.
Control Sequence
Programming the multiplexer involves sending a start condition followed by the device address and a control byte. This control byte determines which of the four channels is active and configures the interrupt behavior. The device supports a hardware reset function through the power-on reset circuitry, which initializes the switch to a default disconnected state.
This ensures that no downstream branches are active during startup, which prevents any unconfigured sub-buses from loading the main bus or causing conflicts during initial boot-up.
Parametric Verification
Testing the device focuses on measuring the on-resistance of the internal pass transistors and the propagation delay between channels. These parameters are evaluated under varying supply voltages from two and a third to five and a half volts. This confirms that the switch introduces minimal distortion to the digital signals across the full operating range.