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Answer
There are a number of issues that can prevent the RAMP development kit hardware or ConnexLink unit from functioning in your application. Here are a few:
- Null Modem Adapter/Cable: The Laird RAMP radios are DCE (Data Communications Equipment) devices. Typically, devices like PCs are considered DTE (Data Terminal Equipment) devices. Peripheral devices are classified as DCE. A DCE device can interface to a DTE device using a straight-through serial cable, such as the cable which ships with the development kits and ConnexLink units. When interfacing between two DCE (or two DTE) devices together, a null modem (or crossover) cable (or adapter) is required to swap pins and convert the signals accordingly. Therefore, if your end device hardware is a DCE (Data Communications Equipment) device, a null modem adapter or cable is required between your end device and the development kit or ConnexLink unit. The null modem adapter crisscrosses the TXD pin with the RXD pin, the CTS pin with the RTS pin and the DTR pin with the DCD/DSR pins. Null modem cables/adapters are available at most computer equipment retailers.
- System Packet Timeout: In applications that were originally designed without the intention of using wireless devices, typically the packet timeouts are very short (microseconds). Because of the system latency introduced by the wireless system, packets generally take several milliseconds to deliver (longer depending on the number of retries required). A system with a microsecond timeout will time out on every packet. Oftentimes, the timeout parameter in the software is adjustable and can be increased to account for the radio latency.
- Interface Baud Rate/Parity: The radio must be programmed to the same interface baud rate that your equipment is using. In addition to this, the radio must be programmed to the same data format that your equipment is using. The radio is programmed to use 8-N-1 data format (8 data bits, No parity, 1 stop bit). The radio supports a number of other formats including parity. See the User’s Manual for more details.
- Handshaking Pins: A number of applications use the extra handshaking pins available on the DB-9 connector (such as DTR, DSR, DCD and RI) to signal start, stop and special-case events. The radio can support these pin functions when Modem Mode is enabled in EEPROM. However, sometimes a special cable might be required to get the development kit pins to the right pins on your equipment.