Figure 2-1 Simplified Block Diagram for HVAC Gateways

For the purpose of this report, a simplified HVAC gateway system block diagram is used to illustrate the logic and translation use cases, see Figure 2-1. For a more complete view, see the interactive online end equipment reference diagram for HVAC gateway.

It is common for HVAC gateways to utilize wireless interfaces such as Wi-Fi®, ZigBee®, or Bluetooth® to connect to a local network. In many designs, the simplest method to achieve this is to utilize pre-built and pre-approved modules. These modules often have limited voltage operation ranges, and to support their usage, voltage-level shifters are typically required between the extremely low power processor, often operating as low as 1.2 V, and the wireless module, commonly operating at 3.3 V.

The most common communication protocols used between the processor and wireless interface are secure digital input output (SDIO) and universal asynchronous receiver/transmitter (UART). Each is addressed specifically in the following sections.