Sun Microsystems 60 service manual Serial Port Components

C.1.11 Serial Port

The system unit incorporates two serial ports. Each serial port is synchronous and asynchronous with full modem controls. All serial port functions are controlled by a serial port controller that is electrically connected to the system through the EBus. Line drivers and line receivers control the serial port signal levels and provide RS-232 and RS-423 compatibility. Each serial port interfaces through its own DB-25 connector.

The major features of each serial port include:

■Two fully functional synchronous and asynchronous serial ports

■DB-25 connectors

■Increased baud rate speed (to 384 Kbaud, synchronous, 460.8 Kbaud, asynchronous)

■Variable edge rate for greater performance

■EBus interface

FIGURE C-7shows a functional block diagram of the serial port.

Serial Port Components

Serial port components include a serial port controller, line drivers, and the line receivers.

The serial port controller contains 64-byte buffers on both the input and output. This enables the serial port to require less CPU bandwidth. Interrupts are generated when the buffer reaches 32 bytes or half full. The serial port controller contains its own crystal oscillator that supports rates of up to 921.6 Kbaud.

The line drivers and line receivers are compatible with both RS-232 and RS-423. Two system board jumpers are used to set the line drivers and line receivers to either RS-232 or RS-423 protocols. The line driver slew rate is also programmable. For baud rates over 100K, the slew rate is set to 10 Vdc/μsec. For baud rates under 100K, the slew rate is set to 5 Vdc/μsec.

C-22Sun Ultra 60 Service Manual • August 2001