Repair manual

2-75
THEORY OF OPERATION
2. Small System Computer Interface
The Small System Computer Interface (SCSI - commonly pronounced
“SKUH-zee”) is an industry standard interface defined by the American
National Standards Institute (ANSI). This interface is an optional parallel
communication port that provides high speed data communication link between
the host computer and the Digital Palette.
This optional interface (Figure 2-11) consist of a host interface cable and a SCSI
Board. The SCSI Board when used plugs into the provided connector on the
Logic Controller P.C. Board.
a. Host Interface Cable
The Host Interface Cable is a 50-pin SCSI connector for connection to an
Apple Macintosh (MAC-II) host computer.
This interface cable provides the signal lines that allows the host computer
and the SCSI Board to communicate with each other. The signal protocol
that takes place between the host computer and the SCSI Board only uses
eighteen of the signal lines of the host interface cable; nine control lines
and nine data I/O lines.
Table 2-15 lists and describes the function of each signal line used to
interface the host computer with the SCSI Board.
Refer to the provided SCSI Parallel Interface Specifications Manual for a
detailed description of the communication signals between the host
computer and the SCSI Board.
b. SCSI Interface Board
This SCSI Interface Board is a single interface board which is installed as
an option within the Digital Palette. It uses a decode PAL (SCSIP1), a
53C80 SCSI controller, and SCSI connectors.
For data to be transferred to the Digital Palette, the SCSI Interface Board
configures its integrated controller to establish data transfer
characteristics. While the controller is transferring data from the
host computer to the SCSI bus, it monitors and services interrupts and
processes the previously transferred data from the host computer. As
stated, the maximum data transfer rate is 500 K/second. The actual
throughput data rate depends on the system configuration and the host
computer that is being used, as well as the selected resolution and the
film type of the Digital Palette.