AT&T 3B2/300 Technical Reference Manual page 456

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CM195B/CM195BA PORTS CARD
General
The CM195B/CM195BA Peripheral Port Controller (PORTS) Card provides four separate,
asynchronous serial ports (RS-232C) and one parallel (CENTRONICS) port. Functionally, the PORTS
card consists of the Common Input/Output (CIO) circuits, two Dual Universal Asynchronous
Receiver/Transmitter (DUART) circuits, and a parallel interface circuit. The four asynchronous serial
ports are identified as subdevices. DUART O supports subdevices SDO and SDl; DUART 1 supports
subdevices SD2 and SD3. The DUART circuits are polled by the 80186 Microprocessor. Neither the
DUART or parallel interface circuits can interrupt the 80186 Microprocessor. Drivers and receiver
circuits are used to interface the DUARTs to MODEMS and/or data terminals (RS-232C). The parallel
interface (CENTRONICS interface) is intended to be used to interface a printer. Figure 3-63 is a
functional block diagram of the CM195B/CM195BA PORTS Card.
The CIO circuits include the following:
• INTEL 80186 Microprocessor
• Input/Output
(1/0)
Bus Control
• Identification/Vector (ID /Vector) Register
• Page Register
• Peripheral Control and Status Register (PCSR)
• Local Random Access Memory (RAM)
• Local Read Only Memory (ROM)
• Miscellaneous Circuits.
FUNCTIONAL DESCRIPTION 3-203