The Technobox 4-port Async Communications Adapter XMC is a cost-effective solution for providing additional RS232/RS422/RS485 based async serial ports for a host processor. It is the next generation version of Technobox’s P/N 4960/2012 PMC product, which has been in continuous production since the 1990’s.
A high degree of compatibility for this XMC is maintained with the prior 4960/2012. First, the same genuine 16C554 chip is used for the UART functionality, guaranteeing correct async operation when compared to competitive FPGA based approaches. Second, the port configuration strategy, using jumpers installed by Technobox upon customer order, is identical. Third, the UARTs are mapped into PCI Express I/O space, consistent with Personal Computer COM port practice; reprogramming a PLD can map ports into Memory Space. Finally, the same Micro D9 connectors, as well as PN4 Rear I/O, is retained in this XMC. Access from the 1-lane PCI Express interface is accomplished through a PCI Express to PCI-bridge. The local parallel PCI bus is then adapted to the 16554 quad UART interface using a PLD on the board. Thus, to the user, it will appear that the COM ports are located behind a PCI-to-PCI bridge.
Unlike the 4960/2012, there are no mechanical interrupt switches to steer the individual UART interrupts to INTx (x = A, B, C, D) for the PCI bus. All UART interrupts are posted on the INTA line by default. However, there is a programming technique, that is also deployed on other Technobox Async adapters, to steer the interrupts via software to the desired interrupt request levels. It is believed that most 4960/2012 users have all UARTs directed to INTA, so change is unlikely. Also unlike the 4960/2012, this XMC only requires +3.3V power rail. The RS232 interface chips generate elevated voltages, which were provided by +/-12V rails in 4960/2012, using built-in switched capacitor voltage multipliers.
Each port is independently set-up by Technobox to operate at either RS232 or RS422 levels. In the RS422 case, an additional option is provided to transmit data on the receive data line in an RS485 fashion. The port configuration must be specified when ordering.
4-port RS232 / RS422 / RS485 Asynchronous (Async) Serial Communication Adapter XMC I/O Card (VITA 42) with PN4 Lead free RoHS Compliant Industrial Temperature 7254