Hardware Reference Manual
PMC422 and PMC422/FP Eight Port serial Controller
2 Theory of Operation
The PMC422 and PMC422/FP are flexible solutions for integrating multiple serial I/O channels onto an SBC
(Single Board Computer). Efficiently packaging eight channels onto a single PMC makes effective use of the few
PMC locations available. Routing I/O to the rear (via the ‘J4’ connector to the host card) enhances flexibility in
developing economical and non-intrusive cabling solutions. Each serial port is implemented with an independent
UART (Asynchronous Receiver and Transmitter) with a separate programmable baud rate. Accessing the UART
controllers via PCI integrates more effectively to modern SBC implementations than proprietary or legacy devices.
Traditional UART controllers are limited to 8 bit access, incurring all bus protocol overhead for every character
transferred (and control operations). The Octal UART utilized on the PMC422 and PMC422/FP support 32 bit
transfers, allowing four characters to be transferred in a single bus operation. Reducing programmed I/O
operations is critical to achieving good performance in PCI systems. While the extended transfer options offer an
opportunity to maximize performance, in many cases the first (and sometimes only) criteria is software
development and integration. The 16C550 register set definition is in common usage for serial I/O devices in all
environments. Maintaining compatibility with this de facto standard, can markedly reduce the time required to
integrate the PMC422 and PMC422/FP into existing software environments. Having the software integration
based upon earlier drivers reduces the risk of unexpected (and undesirable) changes in application interfaces,
which can be critical when creating an evolutionary improvement to existing systems.
2.1 Functional Description
The architecture of the PMC422 is illustrated in the block diagram. There are two major components:
• Octal UART. This single device incorporates all 8 UARTs with a PCI interface. It connects (via the PMC
connectors) to the PCI bus on the host card.
• Signal Drivers There is one driver per UART channel. The Signal Driver controls the electrical signaling
protocol for the channel. Signal protocols supported are: RS-232, EIA-530, RS-422, RS-485, and RS-489.
Operation is controlled via on card DIP switches. Each pair of UART channels is controlled by one
configuration switch package. Thus, up to four different signal protocols may be configured.
There is an eight bit input port on the Octal UART Controller that is connected to a pair of DIP Switches. This
feature may be used to create a system ID, or other configuration input for use by application-specific software.
2.1.1 Outputs
Each UART channel has four signal pairs:
Tx - Transmitted data from the UART
Rx - Received data to the UART
RTS - Ready to Send Output from the PMC422 when the UART RTS is asserted
CTS - Clear to Send Input to the PMC422 routed to the CTS input of the UART
DDC No. Rx-URMH 069 Rev B
Issued 29 October 2003
6 of 25
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