code: func (m *MCP23017Driver) getPort(portStr string) (selectedPort port) {
  	portStr = strings.ToUpper(portStr)
  	switch {
  	case portStr == "A":
  		return getBank(m.MCPConf.Bank).PortA
  	case portStr == "B":
  		return getBank(m.MCPConf.Bank).PortB
  	default:
  		return getBank(m.MCPConf.Bank).PortA
  	}
  }
docs: // getPort return the port (A or B) given a string and the bank.
  // Port A is the default if an incorrect or no port is specified.