RF3500 Seagate Rimfire VMEBus SCSI Host Adapter

The Ciprico Rimfire 3500 VMEBus SCSI Host Adapter is a high performance dual function SCSI host bus adapter and floppy disk controller for the VMEbus. Including the Rimfire 3500 itself, eight SCSI bus devices (target ID values) are supported. With the optional floppy-disk controller, up to four ANSI X3.80-1981/SA-450-compatible floppy-disk drives are supported. SCSI bus data rates of 2.0 Mbytes/second in asynchronous mode and 5.0 Mbytes/second in synchronous mode are supported, while the floppy port can support data rates of 250 kHz and 500 kHz. System bus transfers can be sustained at SCS I bus data rates with burst rate capability of up to 20 Mbytes/second with minimum memory response time, or 30 Mbytes/second using block mode transfers.

One key to the Rimfire 3500 adapter's excellent system bus performance is the Short Burst FIFO (SBF). The SBF is a proprietary gate array developed by Ciprico and used to interface system buses and on-board data paths. The gate array is 32 bytes deep, 32 bits wide, and contains built-in byte and word swapping logic. The VMEbus interface is also 32 bits wide and supports 32-bit addressing.

SCSI bus support of the Rimfire 3500 adapter includes the use of pass-through commands, providing flexibility in the use of features available from different peripheral vendors. SCSI commands are passed to the board via a system memory resident circular command queue. This technique allows the system to add commands to the queue as soon as they are ready, with no timing restrictions. The adapter can extract multiple commands from the queue for processing; allowing it to overlap SCSI bus operations using the disconnect/reconnect feature of the SCSI bus. Connections to the bus are through the faceplate connectors and support either single-ended or differential bus transceivers.