Chapter 2
Functional Description
Block Diagram
The A2400 is an RS-232/RS-485 converter specifically designed to inter- face D series RS-485 modules to radio modems. To this end the A2400 provides three functions:
1)Perform the RS-232 to RS-485 electrical conversion.
2)Control the data direction of the RS-485 bus.
3)Create hand-shaking signals to control the modem.
A simplified block diagram of the A2400 is illustrated in Figure 2.1. This shows the RS-485 and RS-232 drivers connected to their respective interface pins. The A2400 contains two UARTs (Universal Asynchronous Receiver / Transmitters), one dedicated to each port. The RS-485 port is connected to a UART that is integral to the supervisory microprocessor. The RS-232 port connects to a second UART external to the microprocessor. All data communicated to and from the A2400 on either port must pass through the microprocessor. The micro controls the data flow depending on the content of the data and setup information specified by the user.
The A2400 contains an Electrically Erasable Programmable Read-Only Memory (EEPROM) which is used to store operating parameters specified by the user. The EEPROM will retain the setup data even if power is removed from the A2400. The EEPROM requires no battery and is guaranteed to retain data for at least ten years. The setup data stored in the EEPROM includes the baud rate, address, parity, timing data, etc. When power is applied to the A2400, the internal microprocessor reads the setup data from the EEPROM and automatically configures itself. The setup data may be downloaded with a terminal or computer connected to the RS-232 port.